I'm tempted to say that it's your DD in question, so it's your rules. If you don't want her to watch it then that should be the end of it.
Personally, my DC are almost-3 & just-turned-5 and over the last year have watched a mixture of PG and 12 films - all the Spiderman, Lord of The Rings and Harry Potter ones, for example. Not watched Jurassic Park yet, but if it's in over Christmas as usual they probably will watch it.
My 2 year old (almost 3) won't sit and watch anything for more than 10 minutes anyway, but my 5 year old will happily sit and watch a whole film, even the Lord of the Rings epics. He definitely understands, because he acts them all out later, and my 2 year old will play along acting out bits too.
In fact, the only thing that we've had issues with is Coronation Street. I don't watch it, but my in-laws do. DC were at my in-laws, it was on and there was a scene where Paddy (whoever that is, I think that was his actual name?) gets buried alive by a load of grain. My 5 year old (then 4) couldn't get it out of his head, was very upset by it, had nightmares about it and just kept remembering it over and over again.
The only thing that I can think of is that most films he's watched are fantasy (superheroes, monsters, elves, orcs, wizards...), so they're obviously not real, but Coronation Street seems to be more real.