My son writes lefty and started throwing and batting lefty but when he was around 8 decided he felt more comfortable throwing and hitting as a righty. Let her do what feels most natural and she'll be more likely to excel and have fun. Force her to play lefty when she's not comfortable with it and it will hurt her game and enjoyment. I seriously doubt her being left handed will limit her opportunities except possibly at the highest levels of competition. You're far more likely to limit her future opportunities by forcing her to use her non-dominant hand.