So, after taking Garry's advice, I'm posting my draft of what I plan to put on my settlement application to explain my 10-month overstay in the UK. Since there's a very limited amount of space on the e-fastrack form, I'm planning on this (in answer to Section 9, dates and duration of my visits to the UK):
25-20 Oct 1997; 28 May-August 2003; Sept 2003-June 2004. I did not enter the UK with the intention of overstaying. I made a judgment error due to the circumstances surrounding my husband's US visa application. I now realize the gravity of my mistake.
That's all that will fit! Then when they ask me about it at my appointment, I'll emphasize that I didn't work or use public services while I was there, that I have come to understand how serious an error it was, and that I did it for personal reasons (in order to do all the visa stuff for my husband, who is uselss at that kind of thing, and because I really couldn't bear to be apart from him) not for any financial gain or anything tricksy like that.
How does that sound? I know my reasoning isn't anything very unusual, but it's all true.
All advice is very much appreciated. I'll be applying this week!