Don't know if she is a candidate for surgery or if you can afford the surgery, but with one so young the prognosis for a successful surgery are favorable.
Don't know what envoy is, but here is a link to a homemade diet she may like.
http://www.vet.utk.edu/clinical/sacs...Liver_diet.pdf
Also talk to your doctor about prescribing lactulose which really helps liver shunts because it helps remove the toxic ammonia from their system.
Also, talk to yor doctor about giving cranberry extract because chronic UTIs might be a problem. Here's some info. on using cranberry.
Also you may want to look into a product called Pet Home Check up so you can check for UTIs (among other things) on a monthly basis.
http://www.thepetcheckup.com/
Cranberries and cranberry juice have been proven effective for treatment of urinary tract infections in humans (e.g. cystitis)and bladder stones in animals in a number of clinical trials. Researchers used to believe the action of cranberry juice is due to acidifying the urine and the antibacterial effects of a cranberry component, hippuric acid but recent studies have shown components in cranberry juice to reduce the ability of bacteria to adhere to the lining of the bladder and urethra. In order for bacteria to infect, they must first adhere to the mucosa. Thus, taking cranberry products, the causative bacteria are flushed, preventing their colonization of the urinary tract. The more the patients drinks liquid or takes the extract of concentrated juice, the more effectively the bacteria are flushed out from the urinary bladder.
While cranberry juice/extract is indicated as an effective treatment for urinary tract infections in pets, most cranberry juices on the market contain one-third cranberry juice mixed with water and sugar. Since sugar has such a detrimental effect on the immune system, sweetened cranberry juice cannot be recommended. For obvious reasons, patient compliance may be very poor with unsweetened cranberry juice. Cranberry Extract (Capsules, tablets or powder) give your dog (or cat) the benefits of cranberry juice in easy to swallow forms, without added sugar or artificial sweeteners.
Cranberry supplements can provide you with an exact, pharmacologically effective daily dose with natural biologically active substances against urinary tract bacterial infections. Cranberry extract is high in natural vitamin C and other natural antioxidants (proanthocyanidines) and tannins that keep bacteria (E. coli) from clinging to the walls of the urinary bladder and the urinary tract.
Cranberry is used to prevent kidney stones and “bladder gravel” as well as to remove toxins from the blood. Cranberry has long been recommended for pets and persons with recurrent urinary tract infections (UTIs).
Cranberry prevents E. coli, the most common cause of UTIs and recurrent UTIs, from adhering to the cells lining the wall of the bladder. Cranberry's antiadherence action renders the bacteria harmless in the urinary tract. Cranberry has been shown to reduce bacteria levels in the urinary bladders of older women, which may help to prevent future infections. Cranberry can help people with urostomies and enterocystoplasties to keep them clear of mucus buildup.