Because there is still blood they need to xray and it would be best to ultrasound. This has been going on way too long for vet to not get more aggressive. She is probably in a fair amount of discomfort. Any remaining stones may be too big to pee out.
The urine needs to be cultured.
Cranberry juice will not be much of a benefit in a case like this.
I feel so sorry for you and her.
