Have you tried giving her water while on the toilet. I have seen this a couple of times, though not for quite so long. For some reason, when I first started, I just always started running the water in the sink while the child is sitting on the toilet. And the kids also start brushing their teeth at the same time, so they all have a cup in the bathroom so I just keep giving them sips until they want to stop, or they pee. Also here we have a 10 second habit. They sit and count (or I do) to10 and if they don't pee, they get up. Every 5-10 minutes until they pee. Like you, I don't necessarily stay in the bathroom, just in and out (gotta check on the others, too.)

Okay, so maybe this idea is way too out of the box, but you said earlier that she sees you and her dad peeing, I'm assuming he's standing up. So what if you tried to get her to stand over the floor potty and pee like daddy. Might she go for something like that?