Hi Tammy.

Your Ts appearance does sound very strange, like she's having a sex change or something!

Or could be some kind of hormonal change due to her having a baby? I know nothing about that; I'm just racking my brain trying to think of a logical explanation.
Or, she wants a new look for herself for some other reason. Whatever the reason, I'm sorry because I know it's very scary for you. I'm scared just reading about it.
You've been with her 6 years. That's a very long time, long enough I think, that you can be perfectly honest with her. I would say something like "T, you look different since you came back and that scares me. Can we talk about it?" Then, you will see what she has to say. I don't think that would be rude because this definitely affects your therapy with her. Maybe she will say, "Oh, I just wanted a new look", or maybe she will say something else. You don't want to embarrass her, but I'm sure she has realized that clients are going to notice this change and she should have planned what to say.
I wish you luck. I hope your T will be honest with you. Does she generally disclose information about herself with you?