My cat is 14 years old and is grinding her teeth when eating wet food.

I took her to the vet about 6 months ago, and they have inspected her teeth and her teeth and gums are fine (they actually commented on how good she looked and said that her weigh was stable). The vet said that she may be grinding due to stress! which i find strange, as this only happen when she eats wet food, but not dry. If she was stressed wouldn't she grind her teeth at any time?
I have also noticed that she is losing weight recently, she is really enthusiastic for food, but when I show her the wet food, she turns her nose up. So I have decided to feed her dry food, which she loves.

The reason I haven't let her eat dried food previously, is becase she suffers with urinary infections and tends to not drink enough water when eating dry food. This then causes her urine to be string and eventually leads to an infection. I am hoping that by giving her dried food will stop her grinding noise, and help her gain weight.

Apart from grinding teeth and fussiness over food, she is not acting any differently. Still active, catching mice, not drinking excessively, or grooming more or less.

She is due her yearly check up and booster jab, but wondered if I should be more concerned and bring this forward.

Does anyone know why cats tend to grind their teeth when they reach around 12 years old? Should I be concerned?