Over reacting?

[bright sparks]

I don't think you need to dance around the subject - just ask her straight out. She posted it on a public forum than you have every right to straight up say "so your opening up a daycare??"
You need to look out for your needs too and it's obvious you are going to have to fill a spot. My guess is when/if she actually opens her daycare, she will have no problems pulling her kid without a second thought to how it effects you and your daycare.

I second that country girl. Oh my goodness far to many people are passive. To call her out and ask her straight wouldn't be rude as long as you use a nice tone and don't be aggressive and confrontational, which I'm sure you wouldn't intentionally be but our body language can be a little off when we feel betrayed or annoyed with someone. Don't go around the houses. How much quicker will you settle your mind if you just ask her outright rather than as country girl said, "dance around it" I wouldn't even wait for her to bring it up. Ask her next time you see her and if she denies it, call her out by say, "Well thats funny because I read your post on a forum saying you were opening a daycare and you have also been asking me a lot of questions recently" I would have a friendly chat with her and dig for information like she has been doing with you and she will most likely cave and tell you and then you can have a proper honest conversation about it.

Good Luck!