There are two main types of crystals (struvite and oxilate). The struvite are manageable with diet the oxilates are not generally responsive to diet and surgery removes the stones that form.

Keeping an eye on the urine Ph balance is one way to help monitor the potential for crystals/stones. A very low Ph balance can lead to the oxilates and a high Ph can lead to struvites.

I'm certainly no expert on this, just what I know from seeing it at work, but I don't know much for detail beyond that.

Depending on what your mom's dog had for crystals would depend on which, if any, diet would help. Even with surgery if the dog has a tendancy towards developing stones then they may have to operate again. If a dog has a stone it's very painful, and crystals in the urine are like peeing shards of glass all the time. It's not something to mess around with waiting on.

If it's a diet issue there are some good diets for crystals/stones. At work we have prescribed Royal Canin S/O, and Hills C/D. Seems to me the Royal Canin is supposed to help with both types of crystals, I think the Hills is just for Struvites.

Has the dog had a recent urinalysis done? Do you know which type of stones/crystals were diagnosed previously?