Your edge in yoga, is the place between pleasure and pain - it's the point when you are pushing your muscles as far as they'll go, feeling a deep stretch, but NOT feeling a strain. If you go past your edge, you can seriously injure yourself.
Your edge is a personal thing. Only you can feel it and know when you've pushed it too far. The more you practice yoga, the more you'll get to know your body's limitations and its strengths.
Your edge has to do with your body. Your mind might try to affect your edge and say, "If that girl over there can do it, then so can I." Try not to let your ego take over, without listening to your body first.
Just as your body is different from others, your body is different from day to day too. Some days you might feel really open, and getting into a full split is no problem. And well, other days, your hamstrings might be screaming just from walking.
This girl seems to have NO EDGE whatsoever.
Respect your body and move slowly. Remember that yoga is supposed to feel good. If it hurts - you're probably working too hard.