While in the Underforge, I knocked out Aela to take her blood and she was permanently put into werewolf form. Is there is way I can transform her back?
If you're on the PC, console commands may fix the problem for you: Open the console, click on Aela, enter the command "disable" (she'll promptly vanish), then immediately run the command "enable".
This process worked for me when Lydia got "stuck" in a two-handed combat stance without her weapon, and was completely unable to do anything at all except follow me and get in my way. I've never had your particular problem, but "resetting" followers like this seems to work in a wide range of cases. (Plus, as a bonus, your follower will "level up" as if you had just met her!)