My son pulls 45 pounds out of a 2001 Hoyt magna-tec with the single cam. He is using the Magnus stinger 100 grain two blade.

Other light poundage broadheads I would consider and have him use with out hesitation would be the Steel Force premiun heads, Rocky Mountain tradition, G5's montec or B-52 (much improved model now), Razor cap, Simmons new broadhead, and the Wasp sharp shooter.

You got choices galore but I really wouldn't get too hung up with the broadhead being lighter than 100 grains. In fact odds are that a 100 grain broadhead will give you (her) much better ballance (foc) with her arrows and likley better flight.

You are really limiting yourself when you get below 100 grains.