Just wanted to get a few quick opinions on this whether you reckon this is a flake or if she had a legit problem:

Organised a date with a girl to meet up and hang out yesterday,

It was my idea although she was happy to pick out a day,

We were chatting about it and random stuff the night before over FB

In the end I woke on the day and she'd sent me a message at like 9am (We're meeting at 1) saying that "She had a really bad migraine and just wasn't feeling well enough to come"

She didn't mention rescheduling. Flake or believable? Also any advice on what to do next would be fantastic.

I get migraines. If she legitimately had one, she would both:

1) Not feel like hanging out, and
2) She probably wouldn't be thinking of an alternate date.

I would send her a note the next day saying you hope she's feeling better. After some banter, ask about rescheduling.

Never had a migraine before, Good to know.

Thanks mate.