I know what you mean @leanne, I find confrontation of any description almost impossible - I consider it another of the joys trauma leaves is with. It can be very hard to assert your rights when they've been seriously breached in the past or when you feel shameful or unworthy.
You know her behaviour isn't ok and while, as @ghotiff says, it's important for you to find your voice with her, don't beat yourself up because you find it difficult. Challenging anyone takes some trust that they'll respond well, particularly in therapy when the relationship is so key to the work that you do. You likely find, given how hard it is for you to challenge, that getting to where you can communicate with her about her behaviour in session is therapeutic in its own right. Good luck with it.
You know her behaviour isn't ok and while, as @ghotiff says, it's important for you to find your voice with her, don't beat yourself up because you find it difficult. Challenging anyone takes some trust that they'll respond well, particularly in therapy when the relationship is so key to the work that you do. You likely find, given how hard it is for you to challenge, that getting to where you can communicate with her about her behaviour in session is therapeutic in its own right. Good luck with it.