I personally spoke with several veteran NYC dancers who were at the same events in Europe as I was. They all knew the person who took her around at that particular milonga, and he is very,
very unorthodox, to be polite. He's an oddball of oddballs, has very strange ideas about what milongas should be, and applies them to every single milonga he's at, be they traditional or casual or whatever. He is NOT the best guide one could have to mainstream milongas (being the vast majority of milongas in the world) simply because his perspective is so skewed.
This is the Facebook post he made about her, but I'm not going to summarise his thoughts on the common customs and códigos of milongas. Read the comments with your morning tea/coffee.
She went there because, if I recall correctly, she had attended events (different social dance) at the same venue and liked it. Personally, I believe her friend should have tried to persuade her to go somewhere else if possible, and if not get a group of his friends to be around and at least dance with her, since it is NYC's
El Destino.
Honestly, I've seen a video of her dancing tango with that guy before the incident. Impressive for a newbie, but to be expected from a veteran social dancer, open embrace of course, so honestly I'd be more than willing to dance a three-song tanda with her at a milonga/practilonga, or even four songs actually, since I'm always interested in how people find out about and join tango, so plenty of conversation to fill the gaps. Maybe even drag it out to two tandas, it's always fascinating to talk with tango newbies who are accomplished in other dances.
(If I wasn't being clear enough, no, I don't think she could give me even a hundredth of the quality of pleasure I experience with my favourite followers — or even just my regular followers — but that doesn't really matter.
I wouldn't be dancing with her because I enjoy dancing with her, it'd be because I'm curious why a beginner like her is doing at one of the most "advanced" milongas in NYC, and I simply enjoy learning about other people. And hey, if we're friends, what's the harm in one friendship tanda, unless I'm in a bad mood?)