How do I tell my client that I may not be a good fit for their needs anymore?

I’m a freelance writer who has worked with a client for about a year as a managing editor. I’m a young-ish woman and suffer from adult ADD (diagnosed). I’m starting to feel inadequate in my due to lack of organization and strategic function. I sense her frustration when I’m disorganized or miss the mark. I hate that feeling.

I’m a good creative writer but sometimes have trouble managing projects with many moving parts. I know this is a serious shortcoming but I try to manage it. It’s one of the reasons I work for myself—to pick and chose the things I work on to best suit my ability.

This client and I have different working styles and I feel unable to meet some of her demands. I’d like to talk about this with her and see if we can hash about another arrangement—either terminating my contract, or scaling back into projects I’m better suited for.

How would you approach this? She can be persnickety and I don’t want any bad blood even if we have to go our separate ways.