more than one prequel
Question: I want to do a prequel for my character for before the events in the actual series and it's for the last 10 years of her life. I thought about doing just one book for it then I thought about splitting it into two books but I'm not sure how good of an idea that is because the first book would be the first 7 years and pretty much the same thing would be happening of course it wouldn't be exactly the same but everything that happens would be similar and then in the second book it would be the next 3 years and a bunch of different things would happen so that's not a problem but I'm not sure if I should put it all together into one book or make it into two. Which sounds better?
I would recommend you work out the dramatic arc of this character's story. How much chronological time each book spans is irrelevant.
Think of her story as one big event.
That event will then be divided into four smaller events.
1. Setup: this will establish who she is at the start.
2. Complication: this will bring new challenges that pressure her to change.
3. Crisis: this will force her to make a key decision (whether to change or grow more steadfast)
4. Resolution: this will bring her story to its end.
Sometimes parts 2 and 3 are combined, so you might tell this character's story in one big book, or three, or four. (Two books is also a possibility, but in a two-act structure, the first book tends to end with a situation that is unresolved, and the second book is the resolution.)
Each book (or each of these four stages) will be divided into its own 4-part arc, so that it will contain a complete and satisfying story as well as being but one part in a longer story.
It doesn't matter whether, for instance, the Setup stage takes 7 years of chronological time, or one day, so long as it contains a complete dramatic arc.
Incidentally, you never want "the same thing to be happening." Each part of the story should be a different phase in the story and the character's evolution. That's what makes it interesting.