Ginger has a liver problem

Ginger has been acting strange lately. She is a 13-14 year old diabetic cat. Her blood sugar is high, but not terribly high. She is drinking and urinating lots. I brought her to the vet and she lost 3 pounds. They drew blood and her ALT liver marker was very high - 756.

I am going to tweak her food and insulin to see if I can get her BS down. The vet said she could have an ultrasound done to see if there is anything abnormal. Of course this is very expensive. She could also do a biopsy - she didn't say the cost of this. But it's invasive. I'm guessing the vet cannot make a diagnosis without one of these two tests. But I wonder can they do anything if they find out what is wrong?

Does anyone have any insight on this? We are going to wait a couple of weeks and then retest her blood.