It's not implausible, but it's also not obvious enough to understand why a woman like Pevara would make a life altering change such as choosing the Red over the Green. Give us a reason that is blatant

I actually don't have a really negative view of the Red, or at least no more so than any other Ajah. Sure we had a few antagonists early in the series coming from that direction, but given the situation of Rand being a male channeler who was quite clearly going insane it's easy to understand why so many Reds have a dim view of all men. The Ajah performs an absolutely critical function for the society, and it becomes very obvious why it would be difficult for Reds to allow themselves to truly like men or develop positive relationships with men when their primary function revolves around the necessity of essentially killing men. At some point one has to realize that through the eyes of a Red Sister all men have the potential to turn out to be rabid dogs in a very literal way. Cut to several thousand years of this and it becomes pretty clear that this pre-disposition becomes a primary personality trait in what the Ajah tends to seek out.

I think RJ used the Reds mentality to illustrate the negativity of non-gender balanced society and showed us many unsympathetic characters from the Red ... Elaida, Liandrin, Bonwhin, Tetsuan and at first tried to balance that out with Blues such as Moiraine, Siuan, Sheriam and Anayia who very clearly philosophically opposed the Reds and later introduced the more emotional Greens such as Alanna and Myrelle, but once the story really moved beyond these basics archetypes he began showing us more variety in personality even within an Ajah so we suddenly had Pevara, Silviana and on the flip side we had Merise who was sever and almost asexual along with Cadsuane who was described as typical of Greens, but didn't at all fit into the early vision RJ put out of nearly universally beautiful and mysterious pseudo-warrior-women.

I think the only reason he introduced the idea of Pevara flipping her choice was to be able to give her a reason for secretly learning the Warder bond weave.