As a foreigner (in relation to your characters), Katia probably would only recently have met anyone in the group. She has a natural curiosity to an extreme  (Kuriosity killed the Kat). She is outgoing and talkative,  although she doesn't always say the right thing at the right time.  She also might be a bit of a prankster, given the opportunity. 

As for how everyone met, anything is possible. One option could be that Katia made it to one of y'all's cities, and with no belongings or real direction, was caught with nowhere to live. Someone may have taken pity on her and given her a place to stay for an evening, which likely turned into her permanent residence with or without real permission. 

Another option could be that Katia pulled a harmless prank on one of y'all for, as it is stated colloquially, the lulz. Depending on your characters' point of view, they could have retaliated in a way that got her attention, either by siccing the authorities on her or pulling a prank of their own. With the former, she would be penitent and seek to right any perceived wrongs. Withthe latter, she would be appreciative of the prank and probably be your char's best friend (whether or not it is reciprocated).

[@Cu Chulainn][@Gordian Nought]

Also Gordian, I noticed you didn't add PB to your saves with proficiency. Not trying to be nitpicky, just don't want you to get charmed unnecessarily or get banished while we're fighting a dracolisk and need that restoration. 

Aso, you still add your ability score to non-proficient weapon damage. You only do not do so if you are dual-wielding without the fighting style and it's your off-weapon.

In addition, I'm not sure if Harb's world is different from the standard D&D, but Aasimar are basically celestial tieflings, meaning they age at about the same rate as humans and live only slightly longer. Also, they are built like well-proportiined humans, and I've usually seen Aasimar as slightly taller than average. Having a 4' 7" Aasimar would be interesting, but I'm not sure if Harb will allow a 970 year old one to be considered "young." Of course,  if this has all been ok'd ignore me, just some things I noticed prior to digging into backstory.