She can ask, no harm in that. She doesn't have a particularly strong case - referendums are rare and two referendums on the same subject should be held at least 10 years apart (it's the bugger of not having a written constitution - everything is precedent and tradition). Still, Herself might be in a good mood that day.
My personal opinion - they want to leave, let them. They're a horrible drain on the rest of the UK. Mind, if they think they're keeping the North Sea oilfields, they're a wee bit mistaken - that will be the price for leaving.