You need to make sure they are keeping their arms bent the entire time at first, until she starts learning the straight-arm pullover. If the arms go straight, she will never make it over at first.
Also, try telling her to get her bottom up and over the bar. Sometimes they just chin up to the bar and pull their legs up without actually "pulling OVER". Also, I find that if you tell them to kick their feet toward the back wall behind them, it givs them more of a lift over the bar.
Once their hips are over the bar, many girls have a problem actually sitting up, often because they are shifting their wrists too quickly and are thus unable to sit up. Hold their hands in place and tell them to PULL on the bar (this is usually the point where they want to start pushing down to sit up) and to ROLL the bar up their tummies like they are pulling on a rolling pin.
Also, many parents and coaches alike tend to put downward pressure on their feet or legs to help with the leverage for getting their chest up. This (while seemingly effective during spotting) is actually encouraging the wrong motion. Instead of applying pressure to the back of the legs, help them by lifting their chest a tiny bit as they pull on the bar. Once they make it all the way around, then tell them to shift their wrists and push up tall on the bar.
Bottom line: Don't stress too much. She's still very young and the skill will come
Good luck!