Just got back from the vets.

The vet has said that he couldn't find anything wrong with her. Her teeth and gums look fine, her heart rate and temperature and organs seem normal. She has lost 600gms of weigh within 6 weeks.
He told me that there are many reasons why she may have lost weight, but didn't want to take invasive action at present. So for precautionary reasons, he has given her antibiotic and vit c jab, and asked me to bring her in in 2 weeks time. He would have given her a worming jab, but I have only recently done this.
If she continues to have lost weight in 2 weeks time, then he will take blood and urine tests.

Thank goodness for that!!!

I'm still not sure on why she is grinding her teeth though.