No, she wasn't. She wasn't even revealed in a Famitsu scan or a trailer; the game itself revealed her, and she had very little screen time, as well as very little interaction with Sora.
Tifa better be in Kingdom Hearts III, and wear a brand new outfit, though I guess I could accept her in her classic Final Fantasy VII outfit; as long as she's not wearing her Advent Children outfit again, which I think is not a good look on her. She's the number one Final Fantasy character I want to see in the game. I also think they should remake the first game and add her. She should have seriously been in the first game; how can you put in Cid and not Tifa?!