Ms Riley, 35, told the court her view is that the Corbyn-led Labour Party was 'fostering antisemitism' - and she felt 'affronted' at being called 'dangerous and stupid' following an online row over the issue.
She claims a 2019 tweet published by Laura Murray, a senior aide to the then Labour leader, caused her serious harm.
Ms Murray's tweet accused Ms Riley of saying 'Corbyn deserves to be violently attacked' and called for the public not to engage with her.
The dispute started after an egg was hurled at Corbyn during a visit to Finsbury Park Mosque in north London on 3 March 2019.
After the incident Ms Riley retweeted a post by Guardian columnist Owen Jones about a similar egg assault on former British National Party leader Nick Griffin in January 2019.
Jones had commented: 'I think sound life advice is, if you don't want eggs thrown at you, don't be a Nazi.'
Ms Riley had retweeted Jones' post with the words 'good advice' followed by a rose, the Labour emblem, with an egg emoji.
Reacting that day, Ms Murray tweeted: 'Today Jeremy Corbyn went to his local mosque for Visit My Mosque Day, and was attacked by a Brexiteer. Rachel Riley tweets that Corbyn deserves to be violently attacked because he is a Nazi. This woman is as dangerous as she is stupid. Nobody should engage with her... Ever.'
Ms Murray has told the court Ms Riley was being 'deliberately provocative' by tweeting 'good advice' on the day that Jeremy Corbyn was egged.
Rachel Riley arrives at the High Court for her libel case on May 11
Labour Party staff member Laura Murray (right) arrives at The Royal Courts of Justice
Ms Murray denies defaming Riley, arguing truth, honest opinion and responsible publication in her tweet.
She told the court all the tweets that she had seen were saying 'how can you call Jeremy Corbyn a Nazi?' with none of them saying 'this is a comment on hypocrisy, this is a tweet on double standards'.
Asked if she could see it was a 'pile on', she said: 'The way it seemed to me was that it was a deliberately provocative of Jeremy Corbyn being attacked.
'The tweet about Nazis being attacked, saying ''good advice,'' ''if you don't want to be egged don't be a Nazi''. The way it looked to be was that it was deliberately provocative and designed to provoke a reaction from the left.
'And it was getting that reaction, lots of people were saying ''Jeremy Corbyn's not a Nazi, that's not a fair comparison to make''.
'Given that many, many people were criticising Rachel Riley like this, the purpose of my tweet was to advise people, as many as would listen, ''don't engage with this,'' ''it's a waste of time,'' ''no one gets anything from it,'' ''it's a huge waste of emotional resources''. I could see this was really counter productive. It's just totally useless.'
William Bennett, QC, for Ms Riley, directed Ms Murray to an article in The Sunday Times, which featured a personal Facebook picture of her wearing a necklace saying 'f**k the Tories' with the words 'please no bourgoisie on my profile' superimposed.
Ms Murray said: 'That's definitely not language that I use to people or about people.'
Ms Riley told Mr Justice Nicklin how she believed Laura Murray was aware that the March 2019 tweet would 'encourage more hate'.
She has sued Ms Murray for libel, wants damages, and says the tweet caused 'serious harm' to her reputation.
Ms Murray, who no longer works as an aide to Mr Corbyn, says in her defence that what she tweeted was true, and reflected her honestly held opinions.
Mr Justice Nicklin is overseeing a trial at the High Court in London, which began on Monday and is due to end on Wednesday.
Ms Riley, who studied mathematics at Oxford University, has told the judge that she is Jewish and has a 'hatred of anti-Semitism'.
She said she spoke out against anti-Semitism and thought the Corbyn-led Labour Party was 'fostering anti-Semitism'.
Ms Riley says her 'good advice' tweet was sarcastic and intended to show the hypocrisy of the left wing's 'selective support' for acts of violence against politicians.
She told the second day of libel trial she did not step in and clarify what she meant because of advice on how to deal with Twitter 'pile ons' of angry users from the Centre for Countering Digital Hate.
The court heard reactions from Twitter users questioning whether Ms Riley was linking Corbyn with the Nazis, or whether she was condoning violence.
William McCormick, QC, for Ms Murray, asked Ms Riley to explain what she meant by something being a 'dog whistle'.
Ms Riley replied: 'It was in the middle of a pile on, there were however many people contacting me to tell me I was dreadful, awful.
'Laura Murray then decided to add an extra layer, she's already aware of a lot of anger, a lot of movement.
'To add something to that, another level on top of it, I believe she was aware of what she was doing. People that do this can cause a lot of damage.
'If her intention was to make people not engage, she would have deleted her tweet. I believe it was a dog whistle because the opposite happened.
Laura Murray, pictured with Jeremy Corbyn. Ms Murray denies defaming Riley, arguing truth, honest opinion and responsible publication in her tweet
'To actually choose was that choice, put on record in the manner that she did, in the job she was in.'
In her witness statement, Ms Riley said Ms Murray's tweet made her feel vulnerable to 'physical attack' and she had to review her home security.
She said she believed was targeted by Ms Murray following her criticism of anti-Semitism in the Labour Party in 2018.
Ms RIley said she had not tweeted that Jeremy Corbyn deserved to be violently attacked, and she was 'affronted' at being called 'dangerous and stupid'.
'I had made a sarcastic but in my opinion relevant and important comment in relation to Owen Jones and a few hours later the defendant was spreading it round on Twitter that I advocated violence against Jeremy Corbyn because in her words, I had said that he deserved to be attacked because he was a Nazi,' she said.
'I believe that I was targeted by the defendant because I had been critical of the Labour Party's handling of anti-Semitism.
'It was an attempt to shut me up or to stop people listening to what I was saying by telling people that I was encouraging people to commit violence against Jeremy Corbyn.
'The allegations in the Tweet have made me feel vulnerable to physical attack which is naturally very worrying.
'My view is that the Corbyn-led Labour Party was fostering antisemitism.'
She added that she has become a target of a 'very great deal of abuse' on Twitter after using it to condemn what she saw as antisemitism in the Labour party.
Mr McCormick said in his skeleton argument before the court that the case was not one about anti-Semitism, it was about the 'need for restraint in public discourse'.
It was also about the 'rights of those who see a public statement on an inflammatory topic garnering a reaction which is generating responses espousing violence, to call that statement what it is, based upon that reaction,' he said.
'It is obvious that her tweet would provoke hostile reactions of the kind that did in fact emerge. What the defendant then tweeted was true, reflected her honestly held opinions and was a responsible exercise of her own rights of expression on a matter of real public importance.'
Mr Justice Nicklin, who is presiding over the trial, earlier ruled that Ms Murray's tweet was defamatory in common law because the meaning was Ms Riley 'publicly stated in a tweet that Corbyn deserved to be violently attacked'.
The trial continues.