As long as she has not had any complications with the anesthesia before and is all healed up from the leg amputation and is in good health I'd say she should be able to handle it just fine.
To be on the safe side get a CBC blood panel run first to make sure she is healthy. And consult with your vet too.

Spaying will atually help prevent quite a few problems that may occur as she ages.
The earlier you spay the better it is.