How to tighten up belly after pregnancy?

My girlfriend just had our second child. she is 5'5 and was 130 pounds. she is having a hard time because she still has some flabby looking skin around her abdomen. I keep telling her that she looks great, (she really does) but she would like to tighten that up the best that she can without going through rediculous surgey. my question however, is there anyone who knows a good workout that she can do to help tighten everything up? shes not looking for a six pack, but would like to tone up and get as close to normal as possible. i would appreciate any advice on a good workout regimen.