Bitcoin is more than just Forex (due to lack of a central bank), especially once things like Rootstock (smart contracts) come into fruition. But that explanation was pretty good for someone who has absolutely no clue about Bitcoin (your mom in this case).

Just make sure she knows that she could lose a significant portion if things go bad and that she should mentally prepare for that scenario. I don't think it will happen, but it's best to be prepared anyways.