Help with brand new CNA

I'm new to a facility and a new ISH nurse. Recently our facility graduated some new CNAs and one has come to work full time on my hallway. She'a a great girl who is excellent with the residents. The only problem is that she is exceptionally slow. She has been on the floor for a month now and every single night I work with her, the slower she seems to get. Tonight was particularly rough, at end of shift she still had 4 residents who needed washed up/dressed for bed/put into bed, ect. Her rooms were a mess, linens not cleaned up, briefs left in rooms and this was after I alone had taken care of 3 of her other residents including a shower. I'm highly involved with actual care. I toilet, I shower if possible, and I have no problem helping with night care, but it's becoming a problem when I have to struggle to complete MY work on time in order to help her complete hers. My question is how can I approach this with her and help her out? I truly believe that she has the potential to be a wonderful CNA if we can just get to the bottom of her issues. Any time I try to approach her she just tells me "I know my job, I'm just slow." Does anyone have any suggestions on how I should handle this? A self identified weakness of my definitely falls into the supervisor roll I've taken on so I'm somewhat at a loss and still learning on how best to handle situations like this.