having turned up in the States, as you say - and had someone said this was an example of late C19 ABP glass - I would have accepted that without much question - it does fit the bill in most areas, although coloured overlay ABP Rock Crystal is far less common than clear examples.
Regret I can't help with attribution, but would certainly not rule out ABP - some of their cutting in Rock Crystal style was superb - although equally it may well be European.
My opinion regarding the flower is that this is a stylized passion flower of some sort - those long pistils are characteristic of that group - but whether that helps or hinders the quest for origin I don't know. Presumably this is full lead glass.
Not that it really makes any difference, but might be of some limited use to provide the height, and curious to know if there is any wear at all on the underside of the foot.
I've had a quick trawl through Spillman's 'The American Cut Glass Industry', without any joy, and can't see this particular engraved design in Hajdamach's '20th Century British Glass' ..... both books contain a fair amount of Rock Crystal examples - most in clear as you'd expect, and floral decoration was a common theme on these pieces.
Best of luck and hope someone is able to help - truly beautiful drinking glass - not that I'd dare us it.