Try new things and keep track of how well they work. Don't worry about whether your process looks like any other writer's process.
endings
#113: Getting Beyond the Beginning
What I don't recommend is beginning at the beginning. Since you need an ending to work toward, begin with that ending.
#92: How to End a Story
Endings do need to bring at least the major story threads to a resting point, but they're primarily emotional experiences.
#69: Getting Unstuck from “Should”
Every single approach to writing is perfectly okay, as long as it's in line with the kind of writer you want to be.
#40: When to Kill a Character
Adding or subtracting a character in the middle of creating a lengthy work is nearly as challenging as breaking up with a longtime life-entangled partner.
#25: Story Ending Choice Paralysis
Take this significant aspect of your work and see it as a selling point rather than a drawback. Find venues and audiences that appreciate your work for what it is, and keep making the art that you want to make instead of jamming yourself uncomfortably into another mold.
#17: The Three-Quarters Slump
Go ahead, write! You're a writer! Enjoy it! Your book is a mess and that's fine! Many perfectly lovely books start out as messes. Keep on going until you finish your mess.
#4: When Protagonists Don’t Protag
Being a doormat is not something readers generally find appealing in any character, and particularly in a main character. Give her things to do and let her do them. Let her take risks and sometimes succeed and sometimes fail. Let her pick a goal and commit to it and pursue it. Let her, as you say, make choices. Otherwise she isn't really a character; she's exposition with a face and a name.
Story Hospital 