I had this prob with Iain when i changed his milk he was on sma gold n it made him constipated so i changed to aptimil n he was mega sick so i tried C&G Comfort which he was still sick with but not as bad but it made his pass blood in his stools which lead to alot of worry n hosp appointments
Anyway after a few mths we tried him with Farleys 1st milk (yellow tin) n he has been a totally different baby since. No sicky n all the blood in stools cleared up in days. so may be worth trying it.
Hope she gets better soon.