So, have fun while you have her and if it ends move on. It's not the end of the world, you'll find someone else, and maybe they'll be a better fit.
Frankly if some woman said, "I don't think this will last." I'd kick her ass to the curb. Why? Because I don't really want to be in a relationship with someone who has some unrealistic "gut feeling" that she's too scared to voice so she's making excuses as to why things aren't going to last.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."