NTA. As I think we all learned from the season six finale, and season seven premiere of Horsin' Around, people sometimes change, but sometimes those changes don't last. Olivia wanted to go with her birth mother to California because she said she beat her drug addiction, but then the mother relapsed.
Changes are hard and you need more proof that this person has well and truly changed before any discussion about rights or custody can take place. But give her a chance to show you that she's in a stable place now. If it works out, then your daughter can have another adult who cares about her in her life. If it doesn't, then your daughter knows that you still did your best to let her mom back into her life.
But you are definitely making the right choice with not making any decisions with legal consequences yet, otherwise your daughter may have to go on a road trip with Mr. T, Alf, and the cast of Stomp to get back home.