my mom wants to get guppies for her 46g, but there are no other fish that she wants that are hardy enough to cycle with, would guppies be okay to cycle with?
I cycled with guppies and they were fine. However, if you have Danios in a tank why don't you encourage her to do a fishless cycle. You could start it off with the filter media from your tank and as long as you keep this fed (with either ammonia or flake) it will cycle the tank. I did my baby tank that way and it took 11 days.
Good luck, and guppies are great - i'm sure she'll have lots of fun.