What kind of heart testing does she do? SAS? Cardiomyopathy (BCM)? This is of the utmost importance. She should be clear about exactly which tests she does, and provide you documented test results upon request.
As far as not doing hip/elbow testing due to exposure to radiation from the x-ray, that might be the most preposterous cop-out reason I have ever heard. There is very little, and rare, risks of getting cancer due to x-ray radiation. I think I've seen numbers to the effect of somewhere less that 1/2 of 1% of all cancers can be attributed to x-ray radiation. So using that as an excuse is just that...an excuse. Not a valid reason. Red flag #1
Choosing not to test for thyroid dysfunction because they have never seen any history of it in there dogs is an excuse used by many unethical breeder to not perform the necessary health tests. Not "noticing" something doesn't mean it doesn't exists. Red flag #2.
If she is a breeder who belongs to ABC member clubs, then she needs to be working to adhere strictly to the ABC breeder code of ethics. The COE is clear that breeders should strive to improve the breed, and one such way to achieve that is through proactively health testing all of their animals who will be producing the future of this breed. That includes the things she says she doesn't do.
My advice, keep looking. There are many ethical and responsible breeders out there who have not only you, the owner, in mind....but also the future of this breed we all love.
It has been estimated that up to 90% of the ailments which plague our canine companions are diet-related.