I've recently had to go through this with my son. He just turned nine and has only been playing since January this year. He has very good hand eye coordination and has progressed well but has some obvious weaknesses in his game. I was a bit reluctant because almost every other kid has been playing for at least a year longer than him and most are a year older. But he plays a very aggressive and strong game for his size so between his coach and myself we thought why not see how he goes.
We did a lot of expectation management and set some ground rules with him:
1. Chances are you will lose most of your matches so be prepared for this. It is not about winning or losing but finding out your weaknesses and improving them more quickly than you would just being coached.
2. Play your naturally aggressive game and while defensive shots in response to goods shots from your opponent are okay, always play to win. Go for winners, deep shots in the corners, cross courts and drop shots. No pushing.
3. Weaknesses in your game will become evident very quickly. Accept that fixing this may take some time but it will make you a better player.
4. Try to identify where your opponent is weak and target this. Are they bad at backhands? Do they get put off if you approach the net? Start to think strategy.
So far he has only played one round robin tournament but it went well. Lost all four matches as expected but won 25% of the games and took well over half of the lost games to deuce. He was really let down by lazy footwork and unforced errors so we are working hard on these but he played a very aggressive game and hit a lot of unplayable winners. Forehand passing shots, backhand cross court shots and drop volleys. He just isn't consistent enough yet.
So my advice is provided you can keep her ambition in check go for it. The moment she drops her bundle and isn't learning from her mistakes it will all become counter productive. And unfortunately that is what from my limited recent experience seems to happen more often than not, particularly with girls.
Also to me there is a distinct but important difference between a burning desire to win and a desire to make your opponent cry at losing. You just can't define success in sport by the reaction (or lack of) from your opponent. Don't get me wrong, if you can win every game to love then do so. I want my son to have a strong desire to win. But one of the best bits of advice I received as a junior was to only concentrate on what I could control. My technique, my preparations, etc. The moment I started to try to control stuff like the weather, the condition of the court or how the other player reacted I was setting myself up for failure.