Yeah, back legs flopped out, is a sign of being relaxed. The ultimate relaxed position is the dead bunny flop(dbf), and if you ever see it you'll know why it's called that. They really look like they are dead with their whole body flopped on it's side. More than one bunny has freaked out it's owner when in this position
People have had to care for little cottontails before, because of a disability. There was a member on here a while ago, with one that had to have a leg removed because of an injury. I guess if you had to, you could become a registered rehabber if it became necessary, but it probably wouldn't come to that.
It'll be interesting to see how the clicker training goes. You may want to hold off on sugary treats until she is a little bit older. It's usually recommended to wait at least until a rabbit is 12 weeks, to start introducing veggies and treats, and then treats should be limited as they can upset a rabbits digestive flora and cause serious digestive problems. But with your rabbit having been eating fresh foods in the wild, she may not have problems with veggies at her young age. Just always keep an eye out for changes in her poop. If they get soft at all or much smaller than usual and/or irregular shaped, then it means that she is either getting too much sugar and it's upsetting the digestive flora, or she could be having a hard time with a new veggie. That's why it's best to introduce one new food at a time, so that if there is a problem, then you know what food it is and can stop giving it, or reduce the amount. Some veggies/foods can cause gas with some rabbits, so it's good to get to know your bunny's normal behavior, so that if she is ever acting *off* then you will notice it and know that she needs attention. Intestinal gas for rabbits can actually be pretty serious, as it can sometimes lead to a gut blockage. Some signs of pain or discomfort are sitting hunched up and not moving around for a long period of time, changing postitions frequently(laying down and getting right back up repeatedly), eye squinting, teeth grinding, not pooping, and the most noticable is when it's feeding time and your bunny usually comes running but this time it doesn't and doesn't want to eat. You may never encounter any of these problems. It just depends on how sensitive your little bun ends up being, but it's good to be aware of these things in case you do end up having a rabbit that is sensitive at all. These veggie lists are pretty good, and will give you a general idea of how to introduce new foods, and what foods are good for buns.
http://www.3bunnies.org/feeding.htm#greens
http://www.rabbit.org/care/veggies.html
http://www.rabbit.org/faq/sections/diet.html
http://www.bio.miami.edu/hare/poop.html
http://www.medirabbit.com/EN/GI_diseases/drop/Drp_en.htm
It's so great that you are willing and able to care for this little girl. She probably wouldn't have lasted much longer, out there on her own. I'm glad she's ended up in such a good home