Haven't we all been that person at some point, the one who didn't fit in with everybody else all the time? Oh, maybe it's just me.
Your friend is a grown-up. You tried something (bringing her into the group) and it didn't work, for whatever reasons. That is okay. The "group" has a right not to add new members that they feel don't "fit". When I'm part of an intimate circle, I don't necessarily like to include newbies. Everybody doesn't have to hang out with everybody else.
Now, another grown-up approach would be to ask your friends if they could learn to speak up for themselves. Unless your friend is overbearing and boisterous, I don't understand why they couldn't just clear it up in the moment. It's usually awkward while you're feeling each other out. It takes a few times to establish boundaries and expectations. Maybe they don't want to put in that kind of work. It doesn't necessarily make them bad people.
Maybe you can tlak to them about that and talk to your friend, ask her to stifle her personality a bit until everybody's comfortable. OR you can all just decide that it didn't work and move on. If you want to hang with the circle, do it without her. If you host your own event, you can invite whom you want, and maybe they'll see your friend in a more comfortable setting and gain different perspective. Either way--pregnant or not--your friend is a grown-up who should understand that not everybody is going to enjoy her company every time.