Syncope, I think I recall reading in a previous post that you've learned all of Tifa's Limits up to this point. If that's the case, I likely have bad news. Although I hesitate to say this for certain, I've read that there is a known glitch where a character or characters, for whatever reason, cannot learn their Level 4 Limit Break(s). I've played through FFVII many times, but have yet to experience such a glitch, so I can't personally confirm it. I expect there is information on GameFAQs that would elaborate on this, and offer a solution if there is one.

Best of luck in teaching Final Heaven to Tifa.