Hi there
It may take some time to get Bitsy used to having you do her topknot but it can be done
I notice in your avatar pic she's cut short through the body so you probably spend less time than average on her grooming. To get her used to sitting still long enough for you to get the topknot in try brushing her during quiet times when she's relaxed. Make it a good experience & soon she'll be much better about it. The key with this & sooo many other things about our pups is consistency. I'd try just a very little of her hair at first too if she's not used to having it up.
Good luck!