It sounds like she’s shedding. Abnormal hairless due to mites or a fungal infection compes with compromised skin. If her skin looks fine, feels smooth and there’s not a lot of dandruff or areas of the skin  that feel “thickened” (easier felt than seen), this is in all likelihood a normal shed.

Buns can shed in a variety of patterns and often get moultlines, because the undercoat hair (the “wool”) and the guard hairs fall off  and regrow at different rates. Some buns shed in patches so that bald spots form, some buns start shedding on one body part and when that is done, the shed moves to other body parts. The bun can look very moth-eaten while its going on.

Since your bun is 5 months old, the fur that grows out will be a bit different from her baby fur.  You may see changes in color and in texture. This is perfectly normal too.