I think alfalfa is generally a good feed, if fed as part of a balanced diet. I wouldn't want to feed more than about 1/3 of the ration as alfalfa generally. It's high protein & calcium, among other nutrients, so that needs to be taken into consideration when working out balance. FeedXL.com is one good source for diet & nutritional info.
As it's high energy too, I'd be cautious of feeding it to an 'easy keeper' though. But I wonder why you're feeding her Strategy too, if she's already overweight? I know their ad says "without the added calories that can make easy keepers obese." but that same ad says high fat & I imagine their 'controlled starch & sugar' doesn't mean low, with the 'grain products' and 'molasses products' (along with all the other products and by-products on the ingredients list the company site doesn't provide
Especially if you're worried about ulcers/acidosis, I'd personally scrap the Strategy & avoid starchy & high energy feed. If she's got adequate grass, she may only need a low dose ration balancer or such, but especially if you are giving her starchy feeds, it's important to feed it with lots of fibre - chaff, beet pulp, etc - and feed it little & often, rather than only a couple of larger meals daily.