You know she's from an alternate reality when......
a step-by-step guide for Col. J. O'Neill
("He gets confused....." Urgo, 'Urgo')
1. She's got long hair.
2. You can't remember the wedding she has a photo of. (Everyone remembers their own wedding, so no matter how much that guy looks like you, he isn't.)
3. She calls you 'Jack'. (Major Carter only does this in your fantasies.)
4. Kawalsky feels protective towards her. (Any appearance of Major Charles Kawalsky, whose funeral you attended, is a dead giveaway there's something funny going on.)
5. She says she's seen you die. (As, last time you looked, you were very much alive, she can't mean you.)
6. She doesn't wear fatigues.
7. She can't imagine being in the military. (So she can't be your 2IC, can she?)
8. She doesn't recognise Daniel.
9. She kisses you goodbye. (Major Carter only does this in your fantasies.)
10. You kiss her back. (You only do this in your fantasies.)