Give your vet a call and let him know your Maltese is now in heat. You'll likely need to reschedule the spaying to allow normal swelling of the organs to receide, making the surgery easier both for the surgeon and your dog. It shouldn't be too long of a delay, and recovery isn't long at all.
The usual restrictions apply after any surgery: take it easy, and keep up the fluid and calorie intake. My girls have been pretty lethargic for a couple of days after spaying, but quickly bounced back. You'll need to keep her calm until the stitches are removed, and make certain she doesn't try to rip them out on her own. IF this happens, keep her in a crate before and during transportation. You don't want a dog on a leash with missing abdominal stitches to go crazy in the vet's parking lot and end up with her guts literally falling out. If you don't have a crate in that circumstance, you'll need an assistant to fashion a sling around the dog's abdomen while you handle the leash. I'm adding this info here "just in case", and for any readers who find themselves in this situation.
Her heat cycle shouldn't last too long, and small breeds don't make as much mess as the larger breeds. Give it a few days to stop, and another few days for everything inside to settle down. And make sure she has no access to an intact male. :-)