Have them work with smaller, more experienced guys at first who can roll very smooth. I think this is true for all new students though, not just female. If they can handle this (some can't), tell the training partners to stop being so nice. If they can handle this, keep them and let them work together if they like, so long as they go hard. If they don't want to go hard, send them home.
Where I train, we have 1 girl who trains MMA (she's currently a BJJ World Champion at blue belt) and 1 girl who is a legit brown belt (was purple World Champ in 2007 and took 3rd in brown/black this year). If I took it easy on either of them, they'd take my elbow home in their gym bag. Then we have a few ladies who train occasionally, pick and choose training partners, and ask whoever they roll with to not go super hard (one of them really was afraid of getting choked for a while, but she got over it). They are great training partners for sharpening up techniques on the ground, but would never come to Vale Tudo class and I refuse their requests to be their training partner for the 6 weeks before any competition because I need to go hard. That's what works for us at the place I train. Not sure if it helps.