Tara could easily see that Ruby's aura doesn't match her meatsuit and is very black and from helllll and possibly traces of her humanity left over, if Tara's strong enough. Once outed, she won't be shy about showing it. Ruby might be mouthy but she won't be hostile beyond that, simply because Tara is Sam's friend.

I'm not sure how to quite get them there; I can put Ruby pretty much anywhere since she has the ability to teleport. If she makes actual friends with Tara (which will be a feat in itself), it would be more agenda-type friends than actual 'let's braid each other's' hair friends, jsyk. Not that she'd act any different. Ruby's just..."special."