My dog has a scab on her back after an acne-like bump. What is it?

It's quite possible that the little bump on Booboo's back is a cyst. While most cysts are benign (especially ones in young dogs), their size can fluctuate as they fill with fluid, rupture, then refill. When cysts rupture, they can cause little crusts or scabs on the surface of the skin. These lesions can become infected if a dog licks or scratches at the area, but most of the time, they don't cause any problems. I don't see evidence of infection in the picture. For now, I think it's reasonable to keep an eye on the area for changes. If you want to clean it with an antiseptic to err on the side of caution, Hibiclens and betadine are both good over the counter options, but be sure to rinse well afterwards. Unless this lesion gets larger, has more discharge, or irritates Booboo, I don't think you need to take a trip to the vet for this lesion alone. That said, be sure to mention it to your vet the next time Booboo is due for an exam so that they can check it out. I hope that everything goes well!