I don't know anything about teenagers, certainly, but maybe it would help if you described "long and narrow" a little bit better. Like, what size is the hoop you're going to use? Bigger than 5x7? Urban Threads has a lot of wonderful "steampunk" type designs, beautifully digitized, and I'm sure some that would look good on jeans. They also have a blog, with lots of pictures of things they and others have done with jackets, jeans, etc. Might be a good place to start. Best of luck, Marji

A redwork flower or paisley with crystals? Make sure she (we are talking she right?) likes sparkly things before you do crystals.
This link has several long designs.

I suggest you talk to the teenager first!! My 15 yr old grand daughter is so very sweet & wouldn't hurt my feelings for anything. However, I finally realized I was doing things she thanked me for & didn't wear. So now we discuss just what she wants on what!! Saves time & money for me! I've found it depends on what "everyone else is wearing" as to what she wants!!! Good luck & show us what you do!