I have to say, I really struggle with this. It's not a decision I've had to make, really - the only fit-throwers I've had were both under 3, which imo is non-negotiable territory. The youngest I've permanantly turned a child is 3y11m, when he outgrew the Radian by weight, and that was after daily weighings for months (which I don't regret, as it got him to almost 4 instead of 3.5... and honestly wasn't that big of a hassle.) I wasn't going to import for a kid not my own.
I've had two that have eeerf'd (defining that as past 4.) One rode mostly rf, occasionally ff, until just before she turned 5. (At that point she was 34lbs and still fit in a MR by height.) That's when I turned J's seat, and I decided that I needed to get over myself so I turned her. Picked her up from preschool and got a lecture all the way home - "Why my seat like this? I want to sit the other way! You put it in the wrong way!" I turned it right back around, lol.
The other is my current charge, M. She's 4.5 and again, I decided I needed to get over it and put in the seat ff when I started watching her. The subject of "sitting backwards" came up and she thought it sounded awesome. So rf she's been. Like you, I turned her ff for a drive-thru light display, and after that she asked to go ff, but I reminded her that the forward seat wouldn't have her pretty pink cover and she chose rf. At her age, I would have turned her if it's really what she wanted... But since she easily still fits rf, it's not without misgivings. (I also wonder about her bone development, she's got some malabsorbtion of nutrients issues.) I would be lying if I didn't say I breathed a sigh of relief when both girls chose rf.
With your dd, it's all well and good for us on here to say turn her - but I know for me, my "mommy gut" would set off alarm bells and I just couldn't do it. For leg/back pain, maybe, but I really think for me, I just couldn't. If your mommy gut lets you, then I sure don't think it's irresponsible to consider her wishes. Imo, there's a big difference in responding to an angry screaming fit and a genuinely sad kid. Not everyone will agree with that, though.
In either event, at the end of the day, you've done awesome keeping her rf as long as you have!