I didn’t think there’s a specific disorder that results in accent changes. It could be a simple as wanting attention - maybe wanting someone to ask her about it - or it could be she has some psychological disorder.
There is a thing called “Foreign Accent Syndrome,” but as I understand it, it just affects the way your mouth and tongue work in a way that others perceive it as a foreign accent. I don’t think it would cause shifting from one accent to another.
It’s so incredibly short sighted. It’s like your neighbor asking to borrow your hose because his garage is on fire, and saying no because it costs water and doesn’t directly help you. Not only is that going to mean your neighbor is never, ever going to help you with anything, but if that garage fire turns into a raging house fire, your house might go down too.