This is gonna be weird.
Really weird.
This is basically Tribi's timeline. I'll fill in all the gaps in the story, and this won't spoil too much. Sorry in advance!
You can skip this if you don't want to get any spoilers.
She was left in the Everfree Forest at age two.
Her parents abandoned her because she had a massive magical outburst that severely injured her parents.
She as such never got the 'magic inhibitor' to control the baby unicorn outbursts of magic.
She was raised by nymphs and dryads and absorbed some of their magic, giving her longevity that she does not realize she has.
She had very little encounters with pony-kind until the events of MLP: FIM.
She became curious about pony society after the first encounter.
She encountered an alicorn sometime in season one who looked to be about the same age as her, and they both got exposed to a strange plant that altered their minds and bodies to a certain extent.
They then go kill some shit.