If your daughter needs hair accessories to go with her costume for the school concert, consider designing and creating them for her.
They can be created by cutting the plastic bag into strips after cutting off its handles and bottom. Divide each strip, lengthwise, in half and half again. Tie it at the centre with another strip. Arrange it to form the shape of a flower. Do the same with the rest of the strips you have cut from the bag. Join the flowers together by tying the ends together.
A bigger plastic bag will be required to create this head piece. Cut off the handles and bottom. Divide the plastic bag into half and cut at the folded edge. Fold in half again and cut. Fold each cut strip, lengthwise, in half and keep folding till it form a narrow strip. Cut off the corners of folded edge of the strip to form a curved top so that they look like flower petals. Open up the strip and crunch the uncut edge to form a gather. Tie this end up with a rubber band. You can insert a hair clip through the rubber band or clip the piece on the hair using pins.
Following is a version using narrower strips of plastic bag with both ends uncut.
These are actually designs I picked up and adapted from my collection of books for making paper flower. I love exploring by using other materials. The instruction for making this crepe paper flower will give you a general idea of how you can cut your material to form flower petals.
For inspiration, designs and how you can make use of the flowers, take a look at Paper Source.