It's not at all uncommon for an 'outsider' to become more proficient/skilled in a subject,
In this particular case, certainly not. One reason jantango is in BBAA is because she was looking for one particular style of tango that is found nowhere else, and she's developed a strong bias for thinking that what she is looking for (and is emotionally significant to her) is authentic and what she is not looking for is a threat.
That's not skill, that's confirmation bias.
I don't blame her, because it's natural, but that doesn't mean I have to agree with her tango policing or her particular brand of tango fundamentalism.
Most porteños I've ever spoken to are much more laid back about things (they'll often express very strong views but they rarely try to force their view on others, and certainly not other porteños; they believe what they believe with fervour but they're really usually open to the fact others may have other views).
Most hate people dancing in a very open embrace 100% of the time and people not dancing to the music -- I've seen some of them really cringe and suffer mental anguish at some European milongas.
But dancing to Elvis? Naah. They may shrug their shoulders at someone dancing to the William Tell ouverture, but none of them will see it as a sign of impending doom. It's a pity that small digital cameras didn't exist in the '90s when Tete came over to the small Brussels milongas, because if anyone thinks Oscar Casas was Defiling Tango by dancing to Elvis, I can tell you that I'd have material about Tete that's a lot more incriminatory.