Ask your sis to consult with your pediatrician and try to change FM. And choose Prebiotics rich FM.

Consult your baby doctor, it may be some reason, like how much quantity needs to give, what is contain formula milk. You can also talk to your doctor about prebiotics -rich formula milk . my doctor asked me, prebiotics pay a very important role of baby digestion.<br>

Ask her to Consult to her doctor then act.

Go for a formula milk which is closest to mother's milk which contains prebiotics in it which will help in improving gut health issues and leafs to good digestion and improves immunity too

At times babies don't take well with formula milk. Ask ur sister to consult doctor and also change formula milk. Check with your doctor about Aptamil as it's a good milk.