I wouldn't say not interested, more like indifferent. You could take her out once and see if she'll be positively surprised by you, which will get her more interested. She might be trying to play it cool. Or who knows, maybe she'll gain interest. At least she didn't blatantly say no so there's always room for improvement. But if you somehow feel like she isn't worth it, then don't bother.
She said yes. Maybe she's playing hard to get or she didn't want you to think she's very excited. If she wasn't interested, she would have said no. Why not =there are no reasons for me to not go. So I'll go.
Does not = not interested. I say that to be friendly but not too eager. Even if I like you, same story.
I guess is however, uninterested
No. assuming isn't the way to get at things, because were often wrong. If you really wanna know you'll have to ask. Otherwise just taker out to lunch and see where it goes, BUT you gotta assume she's interested because if you assume she's not, it will show on your face and she might perceive you as a boring guy.
"I don't see why not." 'Don't' and 'not' imply two negatives, thus can be labelled as double negatives. Double negatives alter meanings to a positive one. Without the negatives= "I see why." This implies a positive message. In other words, she agreed to see you and may still be feeling indifferent about it.