Just give it some time - it's different for everyone but since she was on a short cycle she should get back to normal soon.

It has taken me up to six months to get mine back.

No need to take anything really unless you are trying to have babies soon.

As Techno said, everyone is different. You just have to give her body time to allow her hormones to get back to normal. Could take three months, could take six months or maybe even longer.
There is an herb that is suppose to help to regulate a females cycle but it may or may not work for her but if you want to give it a shot it's called Dong Quai (otherwise known as Women's Ginseng).