Let her do what she wants to do. If she wants to hibernate she will, even if you keep the cage warm. Not a good idea to disturb them once they go down since hibernation brings about a very slow metabolism and very little bodily functions, not just sleep. Tegus know what they're doing.

Once I see mine go down and stay doen I'll lower the cage temps to mid 70s and that's it. Keep fresh water available just in case she comes out for a look.

Bill