Lady was four when I adopted her, too. Congratulations on taking this little girl in.
The key is to treat her like a puppy when training her. Keep her confined when you can't watch her with 100% undivided attention. Take her out or to her pads after meals, a nap, exercise and praise her like crazy and give her a treat when she goes. She'll get the hang of it.
Lady didn't walk on a leash either. I would go ahead of her and she would take two steps towards me, then sit down. I'd carry her for awhile, then put her down and try again. She got the hang of it pretty quickly, but it was a year before she would walk on grass.
Lady didn't play with toys either and still doesn't. The only toys she likes are treat dispensing toys like her Busy Buddy and Twist and Treat.
I highly recommend the book Secondhand Dog. It is a must have for anyone who adopts an adult dog IMO. Amazon has it or you can get your local bookstore to order for you if they don't carry it.
Amazon Online Reader : Second-Hand Dog: How to Turn Yours into a First-Rate Pet (Howell Reference Books)