Definitely do a trip to the Paediatrician to rule out any other medical reasons before trying some 'behavioural' solutions...

Even to wee 8-9 times in a day would be unusual for a child of that age, whether they are underpants, nappies or whatever...they usually hold on a lot longer...

Common medical reasons would be urinary tract infection, thrush, allergies, irritation. Less common reasons would be diabetes (is she unusually thirsty?)...or a few other kidney and blood things...