Yes, heat the whole limb but you can do it little sections at at time. Yes a form would help, but not absolutely necessary. Heck if you got them to evenly straight, or to match each other it would benefit, imho. Yes, the reflex or part of it may pull back out. If you don't pick up weight, no worries. If you do, you can always tiller it back down. Good idea for s-i-l. In my experience, go for a generous arrow shelf, unless she's an experienced archer. Again, again from experience, 40# @ 26" may even be a touch on the heavy side. Easy enough to adjust it down, if so.
Show us pitchers!