Could you find an appropriate combination of personality and strengths / biases that'd feel appropriate for La Calavera Catrina? 

I feel like there's an overlap with certain other mythological figures but not much and it'd be interesting to see what people think. In fiction she's sometimes depicted as a kind person sometimes a scheming manipulator. https://www.sfgate.com/mexico/mexicomix/article/La-Catrina-Mexico-s-grande-dame-of-death-2318009.php 

For mythology, yes and no I would say. They are so many variations out their that it can be fairly complicated to "lock-on" what a god or otherwordly entity think or behave as. Which is the point - in my opinion - and it might even be interesting to have personas with hidden traits, or that you can discover through events or diplomacy.

Now that I think about it, why do we know the full persona of people you've just met ? o.o

Why only avatar? I thought I could play with La Catrina. I can only setup as my avatar and cannot setup a game with her as AI.

I agree with Aeram. It would be interesting to discover full persona over time.

I mean she could be affinity less... that's one way she could keep her status as a mysterious god.

Sorry I'm a bit confused, the event reward is a avatar 'costume' for Your avatar and not a persona for the AI? Just want to know because the objectives look quite difficult and time consuming so I'm not gonna go for it if I cant unlock her as a AI personality to put some variety in my games.

I got you fam: https://www.games2gether.com/amplitude-studios/humankind/personas?persona=1015311

Stats are based off of the event requirements and, vaguely off of La Calavera Catrina origins as a political satire cartoon.

So this is a megalopolist ai given the lover bias since no other default ai has it (I think). Their strengths are glutton and charmer to aid their megalopolist playstyle. They're cruel to motivate production rush with population, and loyal introverts for thematic reasons.
Introvert was chosen over extrovert to enhance the effect from loyal, so they'll be loyal allies with a few even though their lover bias will (hopefully) make them somewhat popular with most.

This is, of course, a burner account, my main account is Happyhead. Enjoy!

Cool Cool Cool ... as the discord bot might say.