If her Dr. is prescribing D2 she should steer clear. D3 is what she should make sure she is taking. I take (& have taken for some time) 5000IU. Recommended dose by my Bio-Identical Hormone Dr.

1000IU is too low if your levels are low. If it was me, I would take 10,000IU for a while (2-3 mths) and then level back down to 5000IU.

Its my understanding that a level of between 60-80 is best.

This website will help answer both your Questions. Good info. here, for the most part.
http://www.vitamindcouncil.org/

I agree with others about the dosing and if mine was that low I would take 8000-10,000 iu of D3 per day. I would however take it with Vitamins K and A.

This product has all three but she would need to add additional D3. http://www.allergyresearchgroup.com/Vitamin-D3-Complete-Daily-Balance-with-A-and-K2-60-Fish-Gelatin-Caps-p-314.html

The starting dose is 1,000 IU per 25lb body weight, then retest in 6 weeks and adjust the dose accordingly. Ideal range is at least 50mg/dl, or more.

Low vitamin D levels will stop you absorbing magnesium properly as it does calcium. And lack of magnesium can cause kidney stones. I recommend at least 600mg as any organic form, these end in '-ate', like citrate or glycinate.

It's highly likely she's deficient in vitamin A and K as well as the fat-soluble vitamins all work together. Eating liver once or twice a week provides plenty of vitamin A; beta-carotene will not work as 45% of the population can't convert beta-carotene to retinol at all and the rest do so very poorly. Alternatively cod liver oil is also very rich in retinol, Green Pastures brand is best, as most others are rancid before they hit the shelves. They also do one will butter oil which will contain vitamin K2. Or you can supplement K2, best form as MK-4, 1mg is a good dose. Thorne does K2 drops and also D3/K2 drops (http://www.thorne.com/Products/Cardiovascular-Support/Circulatory_Health/prd~KD500.jsp). These drops have an ideal ratio of D3 to K2.

my level was 20, and my doc was ok with me taking 20,000 iu a day. Said that really wasn't a lot of D. So after 60 days of 10,000iu a day of D3, my level didn't rise. But then I started 20k, and added K2 with mk4, in 30 days my level jumped up to 72. I have upped my sunshine, and downed my intake to 10k iu. Will recheck in a couple of months. Also taking it at night makes for a great night sleep!

I can't find the paper now, but it looks like Vit D isn't toxic until you reach the 100,000 iu/day level. I take 10,000iu/day because that's about 10x more than what is recommended (which I think is too low), and 10x less than what looks toxic; so, I have a good margin of safety. I do skip my D on days where I get a ton of sun, though.