I don't know how Gabby was allowed to not pay fees at Excalibur, but I think Chow might let it slide if he truly thought she could go to London. After that, he'd have tons of new gymnasts at his gym, and Gabby would be able to pay with her sponsorship money. Just speculation, though.
She is training one. I hear she at least has it into a pit. Simone Biles is training it too, but is further behind than McKayla.
I can't tell you where I heard that she is training them, it's just something I retained from various Tumblr/blogs/tweets.
I live in Texas, but not in the DFW area, so I can't offer you personal experience, but definitely check out WOGA and Texas Dreams. WOGA is a very established (is that the right word?) gym, and Kennedy Baker lives in Flower Mound and trains at Texas Dreams.