120g for a year old BP does seem quite low, my 4 month (give or take) is 288g and my cb12 boy is 613g. I wouldn't personally remove the hides (no offence to angllady2) I did that once and instead of a feeding response I got a defensive strike and no interest in the food. My pastel is a fussy eater but had managed to put on some weight since I've had her (she was 200g on the 5th October).
The heating techniques sound spot on though, make the rat hot, sometimes I think I don't make them hot enough! You could place her in a smaller tub inside her enclosure with the prey? That was suggested to me when my BP hadn't eaten in a few weeks, I didn't try it myself as she luckily decided to eat just as I was about to try that. Leaving well alone and darkening the room is also a good idea. I have also found that feeding between 10 and midnight gets the better results than trying to feed during the day. I leave my pastel well alone whether she strikes or I have to leave it in the enclosure. I have had to remove the rat 3 times out of the 6 but have managed to get her to eat the other three by zombie dancing, her striking from inside her hide and leaving the rat in the door to her hide that she was in with the head just inside the enclosure, turning the lights out and leaving her until the morning.
I haven't had the issue of switching live to F/T so unfortunately I can only give advice on getting a fussy eater to eat. Maybe it can be transferable? I hope I am giving some sort of helpful advice!
EDIT: at 120g a small rat would be too big, slowly try to increase the feed when you can get your BP eating, very slowly as their weight increases! Good luck