I dislike Sunny (and for that matter, almost every house member lol) and even though I find Sunny's choice of profession disgusting, I do agree with her on that particular point. If you find a man characterless, you should avoid him at all costs and I believe in that whole heartedly. I would never give men who make me uncomfortable the time of day.
HOWEVER, their situation is not at all normal. All of them are stuck with each other in the house for days and weeks on end. Shonali is a contestant there with the aim to get to the finals and win money for whatever reason. She has no friend right now unlike Sunny, Juhi and Sky who have each other for support, irrespective of whether it's real or fake. Plus, she's not a strong person. Nor does she have the ability to convey what she thinks effectively and cannot argue well which is why she avoids conflicts. Giving Amar the cold shoulder would end up threatening her own chances of winning because she would be easily evicted.
Sunny should get a little credit that she finally said something that had not been fed to her by Sky or Juhi. However, we never know and maybe that footage was just not shown. Just like we never saw her actually go and tell Shonali her views to her face.