You need to explain yourself better. Why do you not want to feed alfalfa pellets? You said it's because she's already getting hay. I assumed that meant she's getting Alfalfa hay or a mixed hay that has at least 40% Alfalfa.
If she's only getting grass hay or some other type (no alfalfa), then adding Alfalfa pellets is just fine.
Alfalfa hay or pellets are high in nutrients, amino acids (which are low in grass hay), good calorie content (more than grass hay), and they have quality protein. If you're feeding Select II, then you can ditch the Strategy and feed Alfalfa pellets instead. The only horses that get "hot" on alfalfa are those that are feed a LOT of alfalfa hay (more than 10 lbs a day) or have a sensitivity to Alfalfa (minor feed allergy). Most horses do very well on supplementing their diet with Alfalfa.
You should NOT feed Select II and SmartVite Easy Keeper Grass supplement at the same time, especially when paired with a fortified feed. You can overload her on vitamins and end up with a toxicity (the fat soluable vitamins & mineral). If you want to boost her immune system, look for one of those herbal immune boosting supplements. Adding extra vitamins willy-nilly can do more harm than good.
Is there a reason you WANT to switch her feeds? Is she not doing well? Does she lose shoes? Does she need the max recommended level of feed to keep weight on? Does she get rain rot or thrush more than once or twice a year? Does she have bad "seasons" or is spooky? If you answer no to all of these questions, then there is no reason to change her diet.