I would say its normal. Just keep handling. There is no set size for a boa to be at a certain age. As long as shes not skinny, you are fine. If you are worried, yes you can get a fecal done but that wouldn't be a concern to me. Boas all grow at different paces and just like people, they can have bad days.

I would on the other hand bump her up on feeding a bit. I am feeding my 80-90 gram female nics 2 large rat pinks every 10 days and they are doing great. If you don't feel comfortable going up a rat size, feeding 2 prey items is the way to go.

Hope this helps. I have quite a few young boas still, if you need anything, be sure to let me know