It started off when Tonia commentated her support on Twitter for that new report on women's sport, which is saying things which she has been supporting for years. As a former Welsh cap in Rugby she takes women's sports seriously. There is nothing new in her position the TRAs are so daft they are acting like this is a new thing:
https://policyexchange.org.uk/publication/levelling-the-playing-field/
There is also the important row over the serious sexual harassment in the Welsh Rugby Union which Tonia has been fighting against. It is very serious the Welsh minister for sport has been accused over covering stuff up. Possibly the TRA faction in Welsh Labour are attacking Tonia because she is embarrassing the Welsh government. Details here:
https://www.bbc.co.uk/news/uk-wales-politics-67680854
Tonia and Rosie have been saying the same things for about 4 years now as the most prominent supporters of Labour Women's Declaration. Interestingly it is one of the few times there has been a pile on Tonia, whereas Rosie gets attacked all the time. My suspicion is that Tonia, a former rugby prop, looks tougher, so on some level they are scared of her whereas the TRAs have been infuriated by Rosie because she is as hard as nails, but looks like she might be more easily intimidated. Just more of the massive sexism going on.
There are a bunch of Labour MPs who have openly supported women's rights Diana Johnson is another prominent one, there are a lot more who are covert. Tonia is amongst the most notable in as much Starmer clearly trusts her as she had been a ministerial post till recently and is a whip and has that position for years.
Targeting Tonia is frustrating but actually helps in the long term as the TRAs will alienate the Labour MPs who are trying to stay neutral, but are desperate to win office. For whatever reason Starmer has never been interested in openly supporting Rosie, targeting Tonia is going to backfire, likely to shift the ground in Labour's gender wars in the better direction.
They can't tolerate Young Labour going after a Labour whip for saying things which is Labour policy.