Let's not speculate. "Back injury" can be anything. It's like saying "leg injury". Is it joint, bone, nerve, muscular, etc??? We don't know and all are very different and could range from minor to more serious.
Even though she couldn't go, the fact that she tested it out yesterday suggests (hopefully) it's probably not structural and something less serious like a tweaked muscle. Ever lifted something wrong and pulled a lower back muscle? Did it make you wince when moving around for a while? Yes. Did it cause you life long neurological debilitation? No. No it didn't.
Let's just see how things go and not speculate Stowers year away just yet.