Alot of people around here will suggest wet, not just for seniors, but for any age cat. It helps prevent urinary crystals, and is lower in carbs, which will make it easier to control her weight. Whether you feed dry or wet however, most will tell you to avoid the senior formulas. Alot of times they are loaded with more fillers and carbs to keep the calorie content lower since older cats often arent as active. Its likely better to stick with an all life stages food, and just feed her according to keeping her weight in a safe range. As far as good foods go, Innova, Cal Natural, Felidae, and Natural Balance are popular premium foods that people recommend around this forum. Chicken Soup for the Cat lovers soul is also a pretty descent food, for a good price typically. Either way, your new addition may be used to eating poor food at her shelter, so be careful to do a slow switch over and see how her stomach handles it. For the heck of it, you may want to ask the staff what she was eating at the shelter. If its a good quality food, you can stick with it. If its poor quality, it would probably be a good thing to look for a better food.