My baby's stool has mucus

You don't mention whether or not she is otherwise well. If she is appearing well without other signs, she may have a bit more mucus from the upper airway passing through the digestive tract. Stool mucus can be associated with bacterial infections in the digestive tract as well - often with accompanying complaints of abdominal pain, nausea, fever, or vomiting.

My 2 month old, which was 5 weeks premature btw, was doing well with her similac neosure other than constipation in the beginning then mushy, then started to get looser stools. She had a lot of gas and acted like it was painful to expel the gas so I switched her to similac sensitive but then her stool ended up even more runny and stringy like mucus in it or something. And yellowish. Help!