Liz Buchanan BVSc MRCVS
I suspect that there may be something behind this and would strongly reccommend seeing a vet. You could ask to be triaged over the phone when you make an appointment, so that if the vet wants to see her immediately, then they have the chance to say so. They might ask you about signs of tiredness, weakness or excessive drinking.
Please do let us know how you get on.