My son did the same thing from an early age and still does it occasionally at 21 months! If you notice that she thinks it's funny, it's probably behavioral, as opposed to a medical problem. Next time she gags herself, IGNORE her- even though it bothers you (believe me! I know how agitating it is!) Don't say "no!" Don't pull her hands away from her mouth! Don't even raise an eyebrow. Pretend everything is fine and dandy. She may be doing this to elicit a response from you. Does she do this at the end of a meal? When she wants to come out of the high chair? When you're busy with something else? If so, it's likely behavioral. IF, however, she seems to be uncomfortable and/or she is not gaining weight, definitely go see a specialist! I brought my son to a pediatric G.I. specialist, who prescribed fiber powder in his bottle. He thought that my son was uncomfortable due to an excess of gas in his stomach and therefore tried to make himself vomit to relieve the pressure. It seemed to help. Good luck!