Are you already, or have you been romantically involved with this person already?
When a girl tells you "we have nothing in common.", usually means "I'm not attracted to you, not in that way." Or you haven't sparked her interest, yet. If you have to explain and come off as suplicating, then maybe you should next her. You can also use humor and kind of make her sound stupid and do a sales close on her. Look her in the eye, like a salesman, nod your head when you ask the questions.
What I would do is make the best of it by using humor. Controlled humor, you know, don't be laughin' or smilling too much. Try doing the Ben Franklin Close on her. The one that that's used in sales.
You both do it together. Take a sheet of paper, you draw a line downward. On the left column you two come up with reasons why you both should hang out, or whatever. Put down as many as possible, come up with good reasons, don't hold back, use some humor like some of the lists on the previous posts,
1. We both live in (city, state, etc)
2. We're both...
Do a serious one, then a humor one, be creative.
After each reason, ask her, "you do see how we connect very well when we_______, don't you?", then you move on to another reason on your list. After you have about 6-10. You let her do the right column on her own. At most, she'll come up with two. You then tell her, "Ok, let's weigh the facts, on this column we have, 1-2-3....10 heavy reasons, and on this side we have 2. You have you answer don't you?"
I know it sounds silly, and I'll probably have some posters mock me, haha, but guess what, IT ALMOST ALWAYS WORKS, specially with people who like to over analyze things, people who like "lists", etc. It is a very logical method of makin' decisions. Sounds dumb, specially when you try it on people who've heard it before, but she probably has never heard of it. I've done sales for years and seen it work.
The Ben Franklin Close:
"Most Americans agree that Benjamin Franklin is one of the wisest men who ever lived. In fact, he was the first self-made millionare. When good ol' Ben had a hard time making decisions, this is what he would do.."
Then go into your close. Don't be uptight, hope you get a kick out of it. Ok DJ's, Im ready to take the abuse. Ha.