If they don't trust her, they should atleast trust Geralt. He knows that she is trustworthy, especially if it comes to Ciri, it's a shame he barely shows that...Good question. But we actually have very little information about the relationship between Yen and the rest of the witchers.
Not telling them what exactly she wanted to do wasn't helping either, but as you said, she probably feared that they won't allow it, despite it being the only solution for breaking the curse.Why do you all think, that Yen mistrusts the other (in Kaer Morhen)? If you ask hzer just that, she will answer something like " In the contrary, I fear you don't trust me", meaning, she thinks the witchers will not trust her that the Trial of Grasses is the right thing to do.
She denied his offer just like Geralt did with Triss in Blood of Elves, just much more direct than him. Not really seeing competition there, in general since she met Geralt, another man is just another man and not Geralt. It's the same for Geralt, even though he slept with other women, it's not Yennefer, he even says that out loud.‘I was wondering if you would like to, well...hmmm...as lust would have it...’
‘No, Earl. The past is the past and was not written into the register. Good night.’
It's also interesting that he says "lust". Maybe her main priority in relationships was once lust, but that changed with meeting Geralt, severely. The issue with Istredd already showed that Geralt changed her life for better or worse, but in particular her love life. If at all she lusts after Geralt and scenes like that even shows that.


