Tavia's initial reaction to Vriska is intense confusion. Because she's been assuming her preincarnation was Spinneret Mindfang, ruthless pirate badass (who was not actually a fairy. Or Jesus)! And Vriska is just a thirteen-year old dead girl. Oops.

While Octavia's confusion gives way to massive disappointment, Vriska will be sort of jealous and angry. Tavia has had a cushy life as a weaky-weak soft little Earth human, has been through none of the hardships Vriska did, but people still don't like her and she's still making similar mistakes to her predecessor!

Since they both see their flaws reflected in the other, things would be extremely uncomfortable at best and escalate to screaming hairpulling fights at worst. Both of them would be unable to make excuses for why they are the way they are any more ("I wouldn't be a bitch if I never had to feed Spidermom" and "my life would be so much better if I were a cool hero with amazing powers" no longer fly), and neither would deal with that very well at all.