I think it's a good idea to get her a friend. I don't have experience with rats, but I've seen what just a month of lonelyness can do in a gerbil's mood (gerbils are social animals too). Rats are even more intelligent than gerbils, and need even more estimulation from the environment. No matter how much you play with her, you can't replace a friend from her own species. You can't groom her, sleep with her or be 24 hours with her. From what I've heard, introducing rats is pretty easy, as long as you do so in a neutral environment and clean the cage (and accesories) really really well, to eliminate the smell of your rat (making the cage feel like a new territory for both rats). Of course, don't take my word completely, since I can't speak from experience. There are some other rat owners here that will be able to tell you exactly how to do it, but I'm sure that they'll agree with me that it's the best thing to get her a friend. Good luck!