Food issues with a king

[Lefitte]

So, I've had Eir since early September and I had her on a steady diet of two pinkies every 5-7 days. A couple months ago I moved up to large pinkies/almost fuzzies and she was loving those but my pet store hasn't had them and is now in the process of moving so I'm stuck with what Petsmart has. A few feedings ago I tried to feed her a fuzzy from Arctic Mice and it took some coaxing for her to take it. When she finally did... she regurgitated it up some time after she got it down. Since my temps were normal and it was the biggest prey I'd ever fed her, I figured it was simply too big for her to take. I gave her system a rest before trying to feed her again and went with three extra small pinkies [all my petstore had]. Today, I had some extra defrosted pinkies and chose to feed her however much she seemed interested in. She took 5 and I stopped there [they were small again]. I would really like to move her up in size but I'm not sure what the problem is. She seems intimidated by fuzzies.

What's the best thing to do here? Should I just bump up how many pinkies I feed and how often until she grows a bit more? I know pinkies don't provide much nutrition and very little calcium.

I'll be ordering a scale soon but until then, here are some pictures. Not the best, I don't usually have people to snap pictures for me while I hold her and it's difficult to watch for cats, make sure she doesn't fall, and photograph.

I was told she was 1-2 months when I got her.

First pic is the day I brought her home the first week of September. Second is the first week of October. The last two are from mid-November.