Freud Was Right: Not part of the original baggage, but in modern times it's become popular to give this premise a sexual overtone. Especially in Italy, where the word for "pea" can be used to say "penis".
Fridge Logic: If the girl is SO sensitive that even a pea through 20 mattresses will leave her bruised in the morning, how did she get far enough in the storm to even make it to the prince's castle in the first place? Shouldn't she have arrived a broken and bloody half-dead mess from the rain? (For that matter, how is she gonna have kids?)
It didn't leave her bruised, it was just that she could feel it period. Doesn't help the childbirth fact, but so long as it was just a moderate storm, the kind you wanted not to spend the night in, it shouldn't have been terribly damaging.
No one said she must be good person. The task is made for SpoiledBrats
The Live-Action TV version featured in Faerie Tale Theatre attempted to "civilize" the morning conversation. She was being polite at first and denied the sleepless night when questioned, until challenged to tell the truth, and then she spilled the beans in a more woobieish fashion (especially considering that this version also showed exactly what she went through that night).
One possible interpretation is that it is better to be honest. Though let's face it; the moral is "it is really good to be a princess." Which sucks for the rest of us.
Fashion-Victim Villain: The shoes Laird wanted to wear to his coronation are hideous, and he vowed not to take them off until his vengeance was complete.
Narm: By the truckload. Standout scenes include the awful CG effects when the stained glass figures come to life and at the end when Daria runs into Heath's arms, he spins her around, and then sparkles come out of nowhere as a scene transition.
They Copied It, So It Sucks: The entire plot is lifted from Harold MacGrath's "The Goose Girl", which is ironically based on another fairy tale entirely, albeit the film is a bit more Disneyfied. For example, Hildegard is not a villain in the original book, which makes sense considering the whole being a baby when the switch occured.
The Woobie: Daria has it pretty hard throughout the film. She's taken from her loving father and raised by mean, lazy pig farmers who she has to take care of, she does all the chores on the farm, sleeps in a chicken coop, has the guy she's in love with ditch her, an angry mob tries to kill her, everyone ostracizes her when she goes back to town, and then her uncle and cousin try to kill her.