Could you work on finding a new T while still working with L for a bit? How far along is she in this pregnancy?
Also, it could be that she also wasn't ready to get pregnant again and is also struggling with this in her own ways. But she's trying to be positive about it for herself, and that's how it comes across to you. I'm not sure if that makes sense. Basically, she might be having mixed emotions about it, not all happy.
I will add that no form of birth control (aside from a hysterectomy--as even vasectomies can reverse themselves) is 100%, so it could be she was trying to be careful and was one of the small percentage that got pregnant on the pill or whatever she was using. If it was the pill, if she had to take antibiotics at some point, that can make it less effective that month, for example. And if she did make a mistake, like forget to take a pill or something like that, she could be beating herself up for it inside.
It does sound like it's best to find a new T at this point though (and I'm not one to generally suggest that, but you also said it first). Or at least to find someone with whom you're comfortable to use as a backup while she's on leave and maybe for part of the telehealth time, then consider resuming with her later. Maybe someone who has no connection to her?