Thanks for replying,

No pets were in the house with the previous owners. She's going to the vets today for vaccinations so i'll ask them to check for UTIs aswell, thanks.

I'll get another tray today and see if that helps. It seems she has stopped peeing in the corner (fingers crossed) as she hasn't done it for about 3 days. She can't be trusted to go near the doormat though! I put tin foil down and she just walked over it to an exposed bit of mat and went to defacate on it!

Could it be that she just likes how the mat feels?