Your mom sounds exactly like my dad. When I finally set firm boundaries he pushed and pushed and lashed out at me (fat jokes 2 months post partum, cursing me out while I held my daughter, making a mess then calling me a pig for not cleaning up after him, pissing in drinking glasses and leaving them in the sink, and leaving my daughters room filled with dozens of plegmy snot rags). Now he's banned from my home, because my daughter and husband come first and I don't want my daughter to see anyone, let alone her mother, treated like that. I constantly get messages from him asking when he'll be welcome in my home. If he genuinely apologized (he admits to no faults whatsoever) and came to my city once without stating with us, we might let him back. That's never going to happen.

I feel for you. All I can suggest is state your boundaries and let her know your husband and child come first. She'll probably continue to push, not realizing she's driving you away. As for her already buying the ticket, is there a family member you can talk to about her to help talk some sense into her? I'd also start responding to her wth links to hotels. If she does show up, refuse to answer the door and call the police. Give her a warning this is what you'll do if she chooses to ignore your wishes and disrespect your family, then follow through.