Congrats on entering the world of Morelia.

My first big red flag was that you are trying to feed her every night. I really suggest waiting a few days after offering food before trying again. Constant pestering with it will stress them. I'd give more time to settle in. I had one who would only eat live. Gave him 3 weeks without food, put him in a small tub then into a shelf drawer. Closed the drawer, an hour later the FT was gone and he had a plump mid section. Carpets are easy to get on FT and eat pretty well out of the tank. I do recommend at least a week of settling time before offering food or handling. The real down side with most carpets is that once you start on mice they like to stay on mice. When she's big enough for a rat pink I would offer it and see what she does. If she takes it stick with rats. Your set up doesn't sound bad. If she's only 4 months old a 75 gallon would be way too big. Check out some of the plastic cages available online. So much better than glass. If you give them too much room it will stress them out.
Hopefully this helps. If you have any specific questions please ask.