There are plenty of non-unique cards in the anime. But if you can put in a good explanation on how she got her hands on an Aesir, then that's fine, but only one of them. The thing is, they're too rare and too OP'd to just say everyone have at them. Just like with most of the other unique cards. For example, Shooting Star Dragon (and further, Shooting Quasar Dragon), Red Nova Dragon, the Timelords, the Meklord Emperors, a decent portion of the Numbers, the Egyptian Gods (mostly Obelisk), the Legendary Dragons, etc. That's why I said no unique cards, but the list covered here actually covers most of them. Then there'd be the Accel Synchro and up T.G. monsters because no one's going to know how to Accel Synchro. That's just not common knowledge.
So . . . if you want one of the Aesirs, I'll say you can, but give me some backstory on how she obtained it. I mean, I made an Xyz Teacher who is using a Number monster, but I gave the explanation that he spent years searching to get his hands on even one of them. Then there was someone else who wanted Master Key Beetle (another Number monster). He didn't want to outright give the explanation in his CS, so he had to PM the idea to me. I guess if you had an explanation you would prefer to reveal later, you could PM it to me just the same.
Also, that teacher idea works swimmingly. We don't have a Synchro Teacher yet. :)