I am no expert, but I can tell you what I know.
My mom's dog was very similar to what you are describing when my mom finally started to try to put her hair up. (My mom has a maltese, Suzi) And after helping her I knew when I got my yorkie to start early.
Most likely the problem is that she isn't used to it since she is already a year and hasn't had it up. If you start it when they are really young they can't get it out as easy and learn to like it (in my experience).
With Suzi, we finally started getting it up by one of us holding her and convincing her to be still with a treat she could lick on but not eat yet (so a piece of cheese you can keep a hold of or some peanut butter etc). Then just get as much hair as you can and put it in a loose hair tie. (Like the baby ones that are soft, instead of starting with a rubber band). And just gradually work up to a "better" top knot while she gets used to it. I would also hold off on the bow until she gets used to being put up, since sometimes bows can be heavy and pull their hair.
Also, if she is messing with it A LOT you probably have a few hairs that are pulled too tight. Mine only mess with it a lot when there is something pulling.
Good luck.
