I am sorry that this struggle is so difficult. I really don't think that your T became pregnant and is going on maternity leave just so she can get rid of you. It is not uncommon for women to take that kind of maternity leave, a leave from work, where they don't actually work. It's what she wants and needs for herself and her family; it is definitely not about you.

I'd second the recommendation to look for another T to take over when she's on leave. When my T was on medical leave a few years ago (5 months), I saw someone else in his office. It was helpful to have the support, but I didn't always need it. But it seems a good plan to have support if you do.