My advice is to be 1st AD or line producer. It's her project, she gets to make all the final decisions, you just have to carry them out without any gripes. If she asks for advice, give it. Don't offer unsolicited advice once production begins, mostly because everything should have been thrashed out in preproduction. BTW, that's entirely different than reminding her of scheduling, location, personnel, financial or logistical problems or restraints. Your job is to run the shoot, her job is to be creative.
Your job as 1st AD (or line producer) is to keep the shoot organized and on schedule; her job is to direct. When you get to your next project you will direct and she will be 1st AD/line producer. Then it will be her job to run the shoot and your job to be creative.