What IS This?

I have 10 girls, 9 of which are pretty similar with 1 being totally different. It is this one odd plant that i am worried about. This particular plant was different from the start. She ha much skinner leaves and is more bushy than tall, with many spidery branches.
In the past few days, her leaves have started to really curl up - curl down, I should say - and the sides of the leaves are also curling in and down, towards the leaf midvein. (See Pic 1).
The other 9 girls look pretty good, I think. (Being a first-time grower I can only judge by comparing to pictures I find online. See pics 2 and 3).
All were started from friends' donated seeds, so I have no idea what strains I have. One thing is certain, though, and that is that the one oddball I have is a whole different kind than the rest.
If I had to guess, I would say I am about midway through flowering. Lots of buds, and beginning to make false seed pods.
Environment is as follows:
~ 10'x12' grow room (extra bedroom)
~ Vegged under two 400w MH lamps
~ Currently flowering under two 400w HPS lamps
~ Fox Farm Tiger Bloom added every other watering
~ Soil ph about 6.8
Does anybody know:
1.) What, if anything, could be wrong with the one different plant, and,
2.) What species this one is, that it is so different than all the others.

Thank you in advance for any help you can provide.

I don't have much experience, but leaf curl is often associated with over-feeding. Maybe try every third watering?

Clearly its a root system issue and its rootbound, repot it. The others will start stressing soon to so repot them .