You can be absolutely certain that if you order the
Biotech Pharmacal D-3-50 (50,000IU) 100ct $30.00 100ct $30 you will be getting the most effective, longest lasting most efficient, human form of vitamin D.
I have absolutely not links with Biotech and get no discount or other reward for saying their product is in my view better than ergocalciferol of the same strength.

Whether you get the Biotech or Prohealth $43.49 free P&P really depends on how much Biotech charge for shipping. I doubt p&p is $13.49 but you'll have to find out from Biotech's website. You can always phone them during working hours and speak to a real person.

Only if the Kaiser Foundation Precription is guaranteed Cholecalciferol vitamin d3 is it worth taking IMO.
I am not aware of any 50,000iu vitamin D available on prescription that is NOT ERGOCALCIFEROL.
If someone can prove me wrong they I would be delighted to hear from you and it would be helpful if you could put the product details online so we can share this information with others.
Calcium foodsources. I think you should do both at the moment as it is probable you have both a calcium and Vitamin D deficit to correct. Eating BOTH calcium rich foods AND taking 2 x 500mg calcium daily will not cause an overdose scenario in someone who is currently deficient. When you have proven to yourself and your doctor that you are reliably eating sufficient calcium rich foods then maybe she will let you stop the tablets. Calcium from food is better utilized by the body than calcium from supplements so please do try to get plenty from food. Keep a food log for a few days just to make sure.

The percentage of calcium absorbed depends on the total amount of elemental calcium consumed at one time; as the amount increases, the percentage absorption decreases. Absorption is highest in doses ≤500 mg. So, for example, one who takes 1,000 mg/day of calcium from supplements might split the dose and take 500 mg at two separate times during the day.

This is NOT the same as vitamin D which you can safely take once a week and there will be no measurable difference when compared to the 7150iu daily (except for the baby in the case of pregnant/ nursing mothers.)

I suspect your doctor thinks taking a supplement will be more reliable than relying on you choosing and eating the right foods. So as I think your doctor knows you better than I do you should in this respect do as she says.
With regard to the Vitamin D3 that is the best form and will be more effective than the only form of 50000iu your doctor has available to prescribe.

It is important that you take the same amount as she says you require.

Don't forget the magnesium and maybe also think about some vitamin K2.