She is recruitable in almost any town by speaking with her 3 times with a female main character, then she is recruitable by simply speaking with her. She can use names originated from sweeties(Tart, Candy, etc.).
Tatyana starts out bad, with seemingly no way of combat, she starts with 0 in all weapon levels. And ah, she starts with no WP or JP.
However, her statuses are decent, and promoting her to a Digger or Vigilant isn't a bad idea.
Another downside of her is the Teddy Bear(Kuma-chan), an accessory with cold protection, but it is a forced equipment, this can be solved while doing Tatyana Event.
Her cosplay item, the Guard Blue Edge, boosts her Strength by a measly 1 point, but makes her Dexterity worthwhile, she gets 3 points with this.
Tatyana is good, but growing her in the beginning is so much tedious and frustrating.