Welcome to the forum!
If you haven't seen it yet,
this book is an amazing care guide.
A lot of vets seem to push for feeding Mazuri insectavore food because a few zoos use it, so it's popular on vet-forums. Most breeders tend to favour mixes of cat food. You can find out more on that debate in the care guide, or
in this thread.
Unless there's a really strong reason not to (weight problems that can't be controlled with diet changes), most people free-feed hedgehogs. Although the exact amount will vary by hedgehog and kibble-size, a baby hedgehog will probably eat between 1 Tbs and 1/4 c of kibble per night. Put out a bunch and see how much she eats. The next night, try to put out just a little bit more than she'll eat (so she still has some left over in case of a particularly hungry growth-spurt marathoning night). Replace it with fresh food each night.
Sometimes you have to teach a hedgehog how to use a wheel, and sometimes the wheel doesn't suit the hedgehog. If the wheel feels wobbly, try to secure it so it feels more solid (Comfort wheels are notorious for being wobbly!). If the tilt is adjustable, try leaning it forwards or backwards (this is more common with bucket wheels). To teach her how to use it, put her in it, block her in with your hand, and turn gently. Only do this for a few seconds -- you don't want her to feel trapped or panic! Repeat for a few nights until you're sure she understands how it works.
Hedgehogs can shed; if it's light hair loss, it probably isn't a big concern. If she starts getting bald patches, that's a problem, maybe related to mites, skin infections, nutritional deficiencies, excessively dry skin, etc. Not a problem yet, though, so moving on!
Reduced energy can be a sign of contemplating hibernation. I second Nikki's question about heating and light -- hedgehogs need to be kept warm with steady light/dark cycles to be active. The guide has a lot more information about heating, lighting, and hibernation attempts, or ask if you want more information/links about it.
And, finally... growing is hard work! Quilling is miserable! Yes, when growing in leaps and bounds, and feeling totally painful all the time, sometimes a hoglet will retreat into sleeping all the time. My little guy pretty much just ate, slept, and exuded misery for weeks; it broke my heart! Check everything else to make sure you don't have another problem, but she could plausibly be less energetic because of quilling.
