If on a tight budget, I would look in a few thrift stores for a white or cream jacket that would look good enough. If jacket, take the sleeves off and stitch on some edge tape.
A quilted vest would not be a very difficult or expensive garment to make yourself, otherwise. You would need two layers of fabric, thin batting, thread and a sewing machine.
You could get the pattern by copying a jacket that fits her onto pattern paper - lay out each piece flat and be careful. Make the quilting with the machine.