Yeah, if you're feeding alfalfa pelleted, just make sure it's straight, not molassesed. One handful of sunflower seeds won't go far, unless you mean per feed & will be giving her a fair few daily. Tho of course, she may not need them, or much anyway. Little & often is always best, rather than big &/or infrequent meals. A nutritional supp or such will also be necessary.
I personally subscribe to a service/program called FeedXL.com which is fantastic & invaluable to me, for correctly balancing diets for different horses, as well as a wealth of info on feeding generally & nutritionists available to answer any questions. I highly recommend it, & it's even cheap to subscribe to, to boot! (Yep, I've been told I sound like an ad for them!
) I'm sure there are other similar services, if that one doesn't suit you, if you're interested. Certainly worth looking into, anyway.