My 10 month old still can't drink from a sippy cup?

At 5 months I switched my daughter from breast to pumped bottles. At 6 month I started trying the sippy cup. I just offered it for one feeding a day. She was really messy with it but I figured that was normal. Now at 10 month old she is still incredibly messy with it and generally gives up halfway through her bottle. I offer it at every feeding except the one right before bed where I give her a regular bottle and she finishes that one neatly. I use toppy tippy sippy cups with the soft rubber sippy cap. I like that one because it is interchangeable with the nipples from her old tommy tippe bottles but I have tried others and those are even less successful. Is this something I should be worried about? My pediatrician is kind of pressuring me to make the switch soon.