I have recently rehomed a dog and in just the last week is showing signs of having problems( quite a few medical ones  ).The previous owner never gave me her history,infact she was keen to off load her as soon as possible,poor little girl.Anyway she has ignored my emails asking for her previous vets and im wondering if its possible to find that out through her microchip?

No all that can be found out through the chip is owner's name, address and phone number/s plus e-mail address, and basic details about the dog such as name, breed, colour, year of birth, sex, neutered or not, distinguishing marks, occasionally KC registration number. I'm not sure if they store WHO chipped an animal somewhere, but there's nothing to say it was the previous vet anyway unfortunately.

I guess all you can do is try calling (writing to them might be better?) the vets in the area she lived, explaining the situation, including PDSA/RSPCA. But she may not have been registered under the person's name, or not been to a vet at all! Not impossible the person took her on from someone else then offloaded her to you, the amount of animal dealing going on these days is pretty awful, with rescue dogs being sold on in some cases just to make a few quid.

unfortunatly no thats not recorded altough some might if their pet is on life long medication

As Marianne says, the person who chipped her will be logged by Petlog (if she is indeed registered with Petlog.) So the first thing I'd do is phone them with her microchip number as it may well have been the vets!