While I certainly understand that you don't want to go on a family vacation without your daughter, the trip that you're planning doesn't sound particularly fun for a 13 year old. Since you're not willing to stay back with the younger kids to let her ride the thrill rides with her stepfather, I don't know how much of the trip will actually be enjoyable for her. She'll be stuck following toddler schedules and interests instead of the things she wants to do. Family trips always involve some level of compromise, certainly the whole thing shouldn't revolve around her, but at least some of the planning should be done specifically to hit her "must-dos" if you really want her to come.
Is there no wiggle room in your unwillingness to take the two younger ones by yourself? Could you bring them to the Dis Jr dance show while she and stepdad do ToT and RnR? Or, you camp out in the Dumbo play area with the littles while they use FPs at SDMT and Space? Book your Epcot tier 1 as the Mickey M&G and send them to Test Track? Certainly, you know your kids and your limits. If you're sure that it wouldn't be safe for you to have them alone in the park, then so be it. But, I'm assuming you'll be rocking a pretty good double stroller for your trip. In my experience, kids that age will take long enough to eat a giant lollipop or Mickey Bar for her to have time to do bigger stuff without you having two kids running in opposite directions.