What about velvet coin purses? They're a drawstring square, the velvet helps mute the sound of clinking coings, or you could use them to carry dice and knick knacks. You could make dice from wooden cubes by hammering a nail in just enough to make a dent for each dot, then paint or stain them. I recently made some wooden toggles by cutting a stick into peices the size of my thumb, knick a channel down the middle for the thread/rope and round off the outside edges. Tie the thread at one end to secure. These look so much more true to the period than a zipper or big plastic button! You could also have a go at making either woven or leather belts. If you go with the leather ones you can pick up leather embossing tools pretty cheap on ebay, you just tap the end with a hammer and you can make some really nice intricate designs. Wetting the leather first really helps.
If you pull the knot in the balloon REALLY tight, it keeps that shape for months. I have 2 foil helium balloons that I got for my birthday 9 months ago. They don't float any more, but they are still only a little bit flat. If you want to use paper mache I suggest using a really soft paper, or using well soaked newspaper in short peices so there are no creases, and covering it with tissue paper then a layer of glue to give it a nice very smooth surface. A balloon is made of something similar to latex so would not hold its shape. If you don't mind having a balloon that is a bit smaller, you could fill it up with cold water and dip it in wax until the wax is thick enough not to break without the support of the balloon. The water stops the heat from the melted wax from popping or melting the balloon.
You could make her a cute pencil case with a flat front pocket. I remember being annoyed in school trying to find my pencil sharpener, eraser etc in my pencil case so a pocket helps. You could make her a book bag for her library trips. Where I live you can buy storage cubes that pack flat made of plastic and fabric, these are great because they stack well.
A cookbook of easy cheap recipes would get a lot of use I'm sure! I have a Commonsense cookery book. It's great for someone who is just leaving home because it explains a lot of basic things from making a cup of tea or boiling an egg, to how to do meringues and pies.
Do you know what subject she will be doing? You could make her a pinboard, it would have to be fairly large, but if you use thin ply and wadding it will still be light, and because it's flat it should be easy and not too expensive to post.
These are great! My little brothers and sister are into these too! I'm going to make some as Christmas gift embellishments! (With my family being so huge I always start gifts early. This year I'm trying to do the most difficult people first so they don't get generic "I have no idea what you like here's a mug." gifts.
My first suggestion would be a nice big rug. Pink, yellow or light blue would go nice with that colour. What colours do you like? Are you more into bold or pastel colours? Don't try to hide the carpet under something that you like, but clashes (like red) it just won't end up looking good. A bedspread or quilt with a nice pattern would be good. Pick a large space, like cupboard doors, the bed or the curtains that you can use as a feature to draw your eye away from the carpet. A lampshade is a pretty cheap way to add decoration to your room without cluttering up space. You can decorate it pretty much any way you like!
I would suggest sticking to polyester kind of fabrics if you're going to get wet, most other fabrics will get heavy when wet and weigh you down. You might want to treat them with a flame retardant if you're going through the fire first though.
Craft foam is light and flexible and would make good fins. If you make webbed gloves, kind of like duck feet, that would look cool.