Only eating twice in her first month of life isn't that big of a deal. Twice on pinky mice though might be as they really aren't all that substantial a meal for the vast majority of healthy BP hatchlings. Most hatchings shed about 7 to 10 days after they hatch, they don't eat during that time period. After they shed that first time they'll take their first meal but that can be another week afterwards so that takes up the first couple of weeks of their life. Then it can take a few more weeks to get them well established in a feeding pattern.
Considering she came out of a pet store, you're lucky she's eaten at all - some don't. She looks pretty decent from what I can see in that picture. Depending on her weight either hopper mice or a young adult mouse would likely be good for her.