Hi there, I would look at the NHS web site I posted before.
There can also be concerns if she is a driver (maybe in the future if they continue)
http://www.direct.gov.uk/en/Motoring/DriverLic ensing/MedicalRulesForDrivers/DG_10031252
TIA's can also occur before a stroke (but not always, so don't panic), so you need to get a definite diagnosis. You can ask your healthcare provider for more info on the subject. Stroke is a major concern at the moment, the NHS have infomercials at peak times on tv about the symptoms, so they must have info readily available to distribute.
You need to educate yourself and your Mum as much as possible on the subject, from reliable sources, so you can work out how best to proceed.
I'm sure your Mum is just in a bit of denial as well, although her diagnosis could be wrong if it is unclear, especially as she's not the age you would normally associate with strokes (as in, it's making her feel old before her time). I'm sure if you be a bit patient and show you're worried about her and that you have reliable info about TIAs and anything else it can be, she will come round. It must be very frightening and, as the symptoms are temporary, it's probably easier to pretend it's not happening.
Maybe help her get a definite diagnosis (as in say you'll go with her etc.) so you'll both know one way or the other.