I would get small rubber bands or baby clips that fold open and close and only put up small amounts of hair at first to get her used to having her hair up. Keep an eye on her if you the clips so she doesn't swallow them.
Remeber, she may look adorable in her topknot but it's not a natural thing to them.
Maggie is very much used to her hers now that she won't eat without her hair being up or out of the way. lol
Hot Rod fights it but I think there are times he appreciates having his hair out of his eyes.
You can find packs of small rubber bands and clips at the dollar store. Also you might want to try the soft terry like bands. I don't know what they are called, but they almost look like elasticized terry cloth. They come in all different colors and you get a ton of them for a $1.