Congratulations!
I adopted Lady at 4&1/2. Although they are older, rescues need to be treated like puppies in many ways. Almost all of them have to go back to Potty Training 101.
Treat her just as you would if she were just a puppy. Feed her and take her out on a schedule and praise her like crazy when she goes potty. Make sure you take her out after she eats, wakes up from a nap, etc. Unless you can watch her with 100% of your attention, keep her confined in an xpen. Many people have great success potty training rescues by leashing them to themselves so they can be sure to watch them.
The key is to make sure she potties where she is supposed to because every time she has an accident, it will just make it that much harder. If she does have an accident, make sure you use an enzyme cleaner like Natures Miracle to get the whole stain out or she will be attracted back there.
Rescues require a lot of patience, but it will be rewarded by incredible love and devotion. This is an excellent book for anyone who adopts an adult dog. It will also help you with other issues that can come up with a dog who has been rehomed.
Amazon.com: Second-Hand Dog: How to Turn Yours...