I've not experienced anything similar myself as I don't have kids but I think I might have some comments for you. You seem pretty confident and from your writing I take it quite well spoken, so her saying "this changes things" might not mean something bad, it might simply mean that she is not looking for a relationship with you now (is that what you are looking for?).
For now just role with it, if it comes up again tone the conversation down a bit, tell her a few things about yourself, about your aspirations and such. Swing the conversation to her aspirations and plans (not pushing it towards kids at all!), simply using her confrontation as a path to talk to her about more serious things. I always considered this a good proof of value (DHV) as you show another side to yourself.
One last thing about the text you mentioned at the end. I've started out sending text like that as well but have come to feel that it is very much getting out of the pick-up on your own terms. Which is cheating really

, make her push you away don't just end it because it's easier.
Hope that helps,
Len
PS: Welcome to the community, just joined today myself and also just read your introduction, hope you'll find what you are looking for!