It also depends whether you want to make it for "girls in general", or whether you want to make something special for a special girl.
If it's the latter, making something that the girl actually likes (e.g. a specific animal) is probably a good idea - just because it's more personal and related.
Else here are some models. I'm restricting myself to stuff with online sources, because of your limited time frame. Also, I'm going for slightly stereotypical "girls models". In general, many other designs will be appealing. Below I'm also restricting myself to doable models. I'm not sure which level your skills are at, but I'm assuming you don't want to spend hours on a single model.
Also, I picked models where there's videos available for free. Again, this is because of your time constraints. You probably don't want to puzzle over diagrams, and videos can help.
[I made all of the videos listed below - except for the first -, so it's a very biased selection.]
Alexander Swallowtail Butterfly by Michael LaFosse
It's really nice, easy to learn and you could fold masses of it. See
http://pem.org/origami/ (Fold more models > Origami Now! > second from the right)
Umulius Rectangulum by Thoki Yenn
Modular, fun, and I've always had great reactions to it. It's an easy model to fold, too. It's also not the typical "stupidly girly" choice - I'm relatively certain many would like this a lot.
http://www.happyfolding.com/instruction ... ectangulum
Valentine by Robert Lang
See a video at
http://www.happyfolding.com/instructions-lang-valentine
Not as easy, and slightly more on the romantic side.
Rat by Eric Joisel
The rat has quite a comic feel to it, although again it's not the easiest fold. Paper choice does matter on this model (don't use too thick paper, but alsy try to go for something a bit stiffer).
Diagrams:
http://www.happyfolding.com/files/Joisel-Rat.pdf
Video:
http://www.happyfolding.com/instructions-joisel-rat
Rose Brooch by Sy Chen
Pretty easy, again one of which you could fold quite a few. It's most beautiful with paper that is green on one side and a different colour on the other. Green/white works ok, Green/red is probably the best.
Diagrams:
http://dev.origami.com/diagram_load.cfm ... sebrch.pdf
Video:
http://www.happyfolding.com/instruction ... ose_brooch
Can Love be Squashed? by Sy Chen
Very easy, you could also teach it to the girls if they like. It's a good beginner's model, and very suitable for "mass production". It's also fun, because you can play with it.
Diagrams:
http://www.barf.cc/Hrtsqsh.pdf
Video:
http://www.happyfolding.com/instruction ... e_squashed
Blütenkreisel by Carmen Sprung
Another flower fold, not too hard - but needs relatively accurate folding.
Diagrams:
http://www.origamiseiten.de/eig_2000/o_im05d.html
(Not so good) video:
http://www.happyfolding.com/instruction ... tenkreisel