it could also just be what cereals your giving to her.
mammanuggets
my daughter did this, her vomitng was projectile right after eating, but would be little bits here and there for the rest of the day, got to the point no one wanted to hold her, they were afraid they would get puked all over,i went through several bibs and outfits on a daily basis! I was so worried i took her from dr to dr until i got an answer. Her primary phycisian switched her formulas, took her off foods thinking she was allergic, even thought she had acid reflex and put her on baby pepcid. When nothing worked he sent her to a specialist, who then sent her on to another specialist, i am at this point terrified! in the end they found out her esophagus wasn't closing properly, which is supposibly common in infants and evntually heals itself by their 1st b-day. I know long time but my daughters ended at 8 mths. I would still mention this to her dr b/c it could be that she may be allergic or have acid reflex , but it may just be the esophagus that will heal on its own. let me know what you find out, ill be curious to just how common it might be!
It could be too much food, experts tell us around 6 months is a good time to start solid food and she is 4 months and on cereal or fruit twice a day, maybe cut back to cereal once a day, whilst she is this age.The formula is probably okay, make sure she has been burped on the solid food aswell.