Autocus wont work after rotating focus ring while AF

On some lenses you can use the manual focus ring to override the autofocus while in AF mode, however it seems like this lens doesn't have that feature. When your sister rotated the focus ring, the autofocus motor was still connected to the focus assembly and she put forces on parts that weren't made to withstand those forces in that kind of way. Based on the noise you heard, it sounds like some plastic piece likely broke off inside of the lens, permanently disconnecting the autofocus motor from the focus assembly.

Based on what the lens is worth, taking it to a repair shop would likely not be worth it as you might be better off just buying a used one off of eBay. The other two options would be either accepting that you can only use the lens in manual focus mode, or attempting a repair yourself. Do note that if you were to continue to use the lens there is the possibility, if a piece did break inside the lens, that the piece could potentially migrate to other parts of the lens and cause other issues.

As far as repairing it yourself goes, if you already consider the lens to be a loss then there is at least not much harm you can do attempting a repair. I'd recommend seeing if you can find a disassembly guide or video online. If you can find one, you can partially disassemble your lens to try to find out what broke and if you can fix it or replace the part. Sometimes replacement parts for lenses can be a bit difficult to find though, depending on the lens.