Thanks for the in-depth reply.
Her tub is completely blacked out at sides and I feed her and the room is pitch dark.
Coincidentally I have actually ordered from two different sources and that didn't do the trick.
I do heat to around the temp you recommend. I also dip head in really hot water just prior to offering.
I should have also mentioned she won't strike she prefers to have the rat left in there. I then turn the light of and leave the room.