I am not qualified to give advice on this subject but I am going to anyway. The most critical aspect of freediving is to be with a partner who is always aware of you as you are of them. The great risk is losing conciousness from low O2 before high CO2 makes you surface. This usually occurs with prolonged breathholding after hyperventilation. My ex-partner's best friend died like this on a luxury vacation in Virgin Gorda. Horrible tragedy and they had trouble getting the body back to the U.S. as bribes were demanded to facilitate it. That said- I second letting her pick it out.