This sounds like interesting therapy material to me. Is asking her about her appearance really crossing a boundary? Sometimes I think the client's superego is creating these 'boundaries' and it's more about the client's state of mind than about the Ts boundaries. (I don't know if this is true with you-but this is something I noticed here in general.)

I also say that because I talk about this sort of thing with my T alot. I ask him why he dressed differently, hair, etc. He knows I'm really affected by his appearance. And often it says more about me than it does him. He doesn't let on about his personal reasons most of the time, and we explore my feelings about it. His boundary is simply not telling me what he doesn't want to tell me. I'm free to talk about what I want. Those are the therapy boundaries. Anything's game.

Given your descriptions, I'd be afraid the T who I once thought was strong seems weaker to me. It would prompt feelings about my safety. I'm in psychodynamic therapy, so these types of conversations are common. Aside from therapy material, I do think it's more than appropriate to tell a client if something in their personal life has a high possibility of impacting the therapy.

I understand people work differently but wanted to share how we explore these issues in my therapy. You might be telling yourself it's not ok, while she may respond with concern and interest. You don't know unless you ask, but I can understand if you or others would be uncomfortable with asking.