My 9 1/2 Year Old Pitbull Has An Elevated Alkp

My 9 1/2 year old pitbull has an elevated alkp (2200) drinks a lot of water. She is urinating on herself as well. Seems to be an incontinence problem which she has been on medicine for (proin) all other blood work was normal. My vet wanted to check her for cushings but just to rule it out. She doesn't that've hairloss. Her belly isn't distended. She's also lost 20 lbs in the last 3-4 months. She still eats good. But there is a money issue. The vet reccomended we do an ultrasound to check for a tumor on her liver if it isn't cushings. I can do one test not both. Which would you recommend I do? And do you have any other possible thoughts? Oh and her spleen was enlarged too on her X-ray liver was slightly enlarged but my vet wasn't sure if there was a tumor. Hard to tell by X-ray?