When you lie down with her, is it to read a book or talk about the day, or is it just to cuddle? If cuddling, that can be hard to break. If it's for a book, there's a natural ending point when it's time for you to leave. My son David and I used to sing a song to the tune of "Good Night Ladies" - I substituted his name, threw in a verse about "We had a good day...." and filled in what we did, just cramming the words in to fit the tune, and then did some verses about "It's time to sleep now..." and "Sweet Dreams David..." The song got slower and softer as we neared the end, and it helped relax him.
If you can turn the "war" into a routine in which you lie down with her IF she cooperates, but if she eats up the time with arguing, she loses your "together time", she might get the message. It's tough if this fussy thing has become such a routine that she thinks it's normal. But maybe you can turn it around, that if she can get herself ready in 10 minutes or 15, whatever you think is reasonable (but not too long because she'll fill it with arguments) by brushing her teeth and putting on her pajamas and picking out a book, then you'll come up. Give her a clock or a timer if you need to - something she cannot re-set though!
You are not an awful mother - you are trying to train her to self-soothe! Tell her you know she is a big girl and you want to do big girl things with her, but you are not going to participate in the arguing. You love her too much to fight. You want to have special time with her but she has to let you. She has a choice now, to fight or to have special one-on-one time with Mom. Stick to your guns. After a couple of nights without you at all, she will HAVE to learn to control herself.
Why does she have such a busy and exhausting day? Is it normal, essential school stuff, or is there too much activity scheduled and she just needs more down time during the day? If she is rushing rushing rushing from school to activities to homework, then maybe you could benefit by cutting something out. Kids NEED to have down time, to be creative, to watch butterflies, to learn to fill unscheduled time. If she's got too much going on, then quiet/alone time probably scares her. If she's afraid to be by herself, then the nighttime rituals can be very emotional for her.
Once you figure out what's going on, you will know how to address it and to communicate with her.
Good luck!