Sweet potatoes are HIGH oxalate.
Green beans and carrots are MODERATE oxalate.
Apples are also MODERATE oxalate.
When a dog has a history of calcium oxalate crystals or stones:
High Oxalate foods should be avoided altogether, so no sweet potatoes.
Moderate oxalate foods really should not be given, but if they are, then in moderation...very small amounts and not everyday, but I just wouldn't take the risk.
Watermelon is a great, high moisture treat that you could incorporate into her diet. It will help keep the stones from forming by keeping her diet with more moisture.
Here's an excellent link for you to read through...Keep in mind that not all the foods are okay for liver compromised dogs, but you get the idea...
The article also mentions that veggies should be boiled for lowest oxalate content.
http://www.b-naturals.com/newsletter...late-uroliths/