I think that how much alfalfa to add is something you will have experiment with.
I do know from my own experience of adding too much protein/amino acids, the urine will develop an obnoxiously strong ammonia odor.
The body dumps what it doesn't need thru the urine.
If your horse's urine starts to smell really ammonia strong and/or she starts getting hot or hyper or develops an ugly personality, she's most likely getting too much alfalfa (protein).
Keeping her re-entry work load consistent in terms of hard labor and time will also help, so you can keep her alfalfa consistent.
Meaning, don't work her to death today because you have a babysitter but can only only work her for 15 minutes tommorrow because the baby just went down for nap and that's all the time you have<----if that made any sense at all
While I didn't work my horses, all those years ago, when I had a new baby, I certainly did turn the baby monitor on, go clean stalls and even brush somebody if I didn't hear the baby stirring:) His worst "event" didn't come until he was two and old enough to be at the barn, when he got stuck in the mud by the part we had just re-vamped and his barn boots literally got sucked right off his little feet - lol lol lol lol
Hope this helps some