Mid 70s for dating on your cute dress, Robin. I had a dress nearly exactly like this in '74, although mine wasn't a Miss Rita label. And, yes, I would call those peonies, too.
I would refer to that as a shaped empire waistline; the cut of it would be flattering for the bust-line.
while yours does have neckline detailing, (btw, i would refer to that as contrast collar and cuffs, rather than pilgrim) I wouldn't categorize it as prairie dress, either.
Prairie dresses typically have a bit of a "country" look, often with tiered, ruffled hems; often with attention at the neckline of the bodice, lace ups, sometimes a bit lower cut. And, although some prairie dresses do have insert lace, that is not a requirement for prairie dresses, at all. these would be good examples of "prairie dresses" (btw, not my images, these are just from a google search):
I could see it as boho, though, which is short for bohemian, of course, and refers to the lifestyle of a person who would wear that sort of garment, rather than a set of details of a garment that designate that description. (bohemian: having informal and unconventional social habits.) although some garments can be boho and have flowing sleeves and voluminous skirts, that doesn't mean they have to include those details to be described as such.
