The more she reveals about this engagement, the more I suspect SHE planned absolutely everything.
It seems like she probably picked the date, chose the location, sent him an itinerary of activities, booked everything, bought the ring for herself, etc...and the ultimatum was whether he was going to show up and do it or not. If he didn't, she probably would've turned it into a "I proposed to myself 2.0" trip.
I may be willing to give her the benefit of the doubt when it comes to her motivations for her intense quest to be married and how she's gotten to this particular place, but after watching this engagement video, I absolutely agree with you, and there is actual proof about what you suggest.
At around 8:57, she talks about wanting someone to go out on a limb (watch her eye blinking and lips purse), go pick out a ring (even more intense eye blinking, subtly shakes her head no and looks away, lips even more pursed), spend their money on the ring (more facial movement, widened eyes, odd moment of a widened jaw, with more oddly dramatic blinking) ... dramatic lip pursing, blinking, highly anxious facial cues ... she's trying to hid a lot, here, and is not being completely truthful about the evolution of the planning or her happiness regarding the events. Her facial cues say it all.
At around 9:53, she also does something really strange - she equates marriage to "doing the thing." What. The.
duck. She's not two years old, she can use her words - the fact that she almost infantilizes this huge event in one's life to a noun that literally means "to not give a a meaning to" is truly telling. But just watch her facial cues when she then shows the camera the ring - no weird blinking or pursed lips or looking down or away, and then she admits that "I wanted it to go this way and not that way." No blinking, no facial ticks - I'm now convinced she's planned it all.
When she talks about wanting to be engaged and how excited she is, her facial cues are more open, honest. Her eyes don't lie in those parts, her excitement genuine. But I'm absolutely convinced now that she left many facts out of the timing and planning of this engagement, that's for damn sure.