I already mentioned that if you don't have a scale you can feed to the widest part of the snake's body...
There is no way for us to tell you, you'll have to figure it out on your own unless you offer a photo with some sort of comparison.
Once you fix the vive (get an actual hot spot with a thermostat, add in one or two more hides - especially for a 30 gal. assuming it is glass, cover 3 sides with paper if it is glass, and get a larger size RAT) then your snake may eat.
To offer it, once the rat is thawed (which you can do by letting it sit out on the counter until it is the same temp as the air and there are no hard lumps in the middle) run it under some hot tap water either in a baggy or not, put it in some feeding tongs - you can get those at a pet store - and offer it that way. Try doing a little "zombie dance" or bobbling to entice your snake. Only offer once a week, no more. Even if s/he doesn't take it.
DON'T shove it in her face or tap her with it!