First, my deepest condolences on the loss of your beloved mother. I am not sure if you are trying to settle the estate and/or make bequests or donations.
I do not know how long QVC keeps a record of all purchases (my online purchases are only viisble for a few years), but I would certainly never use that as a barometer for determining the value of jewelry.
Sometimes QVC items are extremely overpriced as compared to the market, and you are paying a retail price. Additionally, insurance values are also high as they allow for complete replacement of the item. If your mother bought gold jewelry a long time ago, gold prices have certainly risen substantially.
You should consider hiring a professional jewelry estate appraiser to review all her jewelry and use current market values. Sometimes professionals are required by probate courts or also if it is a large estate subject to federal estate tax. Using a professional service would be the most accurate way to determine all the values.
Best wishes!