As a therapist: you can change therapists at any point, for whatever reason you wish. This is clearly bothering you so you should find someone new. You don’t have to tell your therapist why, though you can if you like.

Personally, as a parent, yeah... that seems ambitious as hell to me. You can’t predict how the birth will go and how you’ll be doing physically and mentally afterwards, so it seems risky to me that she’s booking people in for so soon afterwards instead of giving birth and then assessing where she’s at. To me it’s akin to knowing you’re booked in for a major surgery and then scheduling clients for 1-2wk later without taking into consideration recovery time. You’re very likely to have to let them down.

I think if her previous childbirth and new baby hadn’t impact your care you might feel differently, but she literally used your paid session time to also care for her infant, more than once. That brought her personal parenting life into your professional work together, which should never have happened. To me that is absolutely wild, there is just no way her attention and focus were completely on you while also monitoring her child, even if they slept the whole time (which isn’t a given). As a therapist that is so disrespectful to you as a client and, imo, unethical. You wouldn’t hold a session as a therapist while working as a barista using a headset, or while catching up on tv in the background, or while cooking dinner, so you shouldn’t while also engaging in childcare. When you mention her having a baby plus toddler it makes me wonder whether you’re worrying she’ll pull the same thing again.

It’s a kind instinct to want to not offend her, but it’s also not something you need to concern yourself with as the client. You can go with a kind white lie:

‘Hi therapist, I just wanted to give you notice that our next session will be our last/our last session is the last one I want to attend. You’ve been so helpful to work with and I can’t thank you enough for everything we’ve worked through together. I’ve decided it might be helpful to see a specialist who deals in trauma going forwards. All the best, OP’

Or... you can go with the truth:

‘Hey therapist. This is a really awkward topic to bring up but I trust our relationship can handle it so I hope that you understand where I’m coming from. I’ve decided to think about seeing a different therapist/bring our sessions to a close. To be really truthful, it wasn’t helpful for me when we had sessions a while back where your little one was present, though I didn’t say anything at the time. I’m a bit concerned that going forwards your new parenting situation might impact upon our sessions in a similar way. I appreciate everything you’ve given me during our sessions and will always be grateful for our time together, and I hope you understand why I’m making this decision. Good luck with everything’