It sounds like an an amazing, beautiful idea, it would be creative and fun for the attendees, and a lovely keepsake for her. What a beautiful thought!

It also sounds like a LOT to organise in just a few days. Quilts are not easy to sew together and have a good finish, ie, neat joins and everything perfectly flat. If you really want to do this, and don't sew at all yourself, I would suggest you find a local sewing/alterations person, and have a chat with her (or him.) You'd want to know the price of having it all stitched together - and it will be time-consuming, I would think even with a machine - before you go out and buy the makings.

If you did decide to go ahead, if you used squares of approx 21cmx21cm, (the 1cm becomes a 1/2cm seam allowance for stitching together) and sewed them as a 6x5 retangle, the final dimensions would be 100x120cm, plus a few more cm for a border.

You'd probably want to use cotton, with the decorated squares one shade or a range of several colours, and a single large piece of cotton for the back, pattern or neutral, plus enough for the border, either precut binding or enough cotton to make 5m or binding - the sewer could advise you how much you'd need as this depends how wide the border will be. You'd then need the fill, and the thread, and the paints/pens whatever is appropriate for decorating. And you'd need to make sure every quare is cut accurately, as if they're a bit skew-wif (sp?) it will make the whole quilt not lay flat.

It's such a lovely idea, I really hope you do carry it out, good luck.