You can just save your eggshells, grind them up in a (clean!!) coffee grinder and use that. The measurement I've typically read is 1/2 tsp. per pound of meat.
You could also get a copy of
Dr. Pitcairn's Guide to Natural Health For Dogs and Cats http://www.amazon.ca/Pitcairns-Compl...2507214&sr=8-1
Which talks about various forms of calcium supplementation pretty extensively.
You can see the cal. supplementation chart from the above book here:
http://books.google.ca/books?id=tEso...vYUUg#PPA67,M1
All that said, there are some pretty decent arguments for why using raw bone (rather than bone meal-which is heated-or other supplements) is preferable, but if it's no calcium vs. not the ideal form, the choice is obvious.
The other thing to maybe stress to your mother is the need for organs, various meat sources, fish, etc. Perhaps doing as you planned and making frozen patties and sending along the recipe would help her figure it out?