I think I have something similar.
Basically my brain will just stop processing input at random. For example, I will be reading a page and then suddenly the words stop making sense. My eyes work fine, I can clearly see the words, but I cant figure out what the words mean. I can reread the same article a dozen times, and still not understand what it said. It is fairly annoying.
This generally only happens when I am overwhelmed, exhausted, or otherwise mentally drained. For example, it never happens after I am well rested doing something enjoyable. It usually only happens when I am operating on 5 hours of sleep, or just got done with a long, difficult day of work/school. The best thing to do in this situation is just to take a break and relax, take a nap if possible. I personally pace back and forth as that helps me relax, but your daughter may have her own solution.
I dont know if this is what is going on with your daughter, but try taking a short break next time it happens. If her brain is getting overloaded, then trying to explain it again isnt going to help reduce the overload. Just taking 5 minutes to walk around the house a few times might help her clear her head.
If taking a break doesnt help her, she may have some other memory problem that I'm not familiar with.