I agree with Lisa, you do NOT have to invite this girl who was practically trying to pull an invite out of you by the sounds of it. Who the hell does that?! Yeesh!
As for your other friend, I really hope she pulls through for you at the end of the day. Maybe she was busy or rushed or had other things on her mind when she said she could see what she would do? I dunno, just thinking out loud. Anyway, best of luck with your wedding planning. This forum is such a treasure for all brides, past and future AND the Dominican Republic is a gorgeous place to have your wedding, I'm confident it will be an amazing day for you!