I have Spondylolysis (cracked L5 vertabrae, but no slippage) and DW has grade 3 (or 1 whichever is the lowest grade) Spondylolythesis (cracked vertabrae that is slipping slightly). Both conditions are quite common, especially in girls that have done gymnastics. Spondylolysis is due to a genetic defect that causes a portion of a vertabrae to be weak. In some cases the vertabrae is cracked at birth, in other cases it can be caused by stress on the bone. The slippage in Sponylolythesis can also either be genetic or caused by stress. It's estimated that 10% of the population has one or the other, but most people don't know that they have it. Most people only find out they have it if they get into a car accident (or some other accident) and have X-Rays taken of their back. And most people that have it never experience any symptoms. The fact that the symptoms are hit or miss makes it very frustrating for people such as myself that experience pain from it. I've been through physical therapy, epidural injections, MRI's, Xrays and bone scans. I had one doctor that wanted to fuse two vertabrae together and I've had two that recommended that surgery should by a last option and that it would be stupid to jump into it at my age (25). It's important to note that all of this was done because I was having extreme nerve pain due to a weight lifting injury and later due to a car accident. I am not considered a normal case of spondylolysis.
As far as what you can do, here's what I would recommend for long term care (you haven't posted details about your DD and her symptoms, so I'll assume that its assymptomatic at this point) to minimize the risk of complications of the future:
1) Maintain a healthy weight. Carrying around extra weight is the worst thing you can do for your back.
2) Regular exercise, especially high repitition weight lifting, is highly recommended.
3) Don't lift heavy weights. I know I just recommended weight lifting, but that is exercising with weights that you can do 10-15 reps of in a controlled manner.
4) Hope/pray that you don't have any problems.
I know that all of these are recommended for everyone regardless of whether or not you have spondylolysis/spondylolythesis, but anyone who has chronic back pain will assure you that the effort put into staying healthy is well worth it.
I'll be happy to answer any questions you have as I've done extensive research on the matter and have visited MANY different doctors for it.
-Josh