Vitamin D?

I've been thinking. File this in the thinking myself into paranoia category, but I'm starting to wonder whether a vitamin D and calcium deficiency might be a problem for us.
Sasha has been breastfed from the day she was born. She's not eating food very well and never has. She will not drink milk. We are a night shift family so our exposure to sunlight is VERY infrequent. This all is the perfect setup for Rickets, a vitamin D and calcium deficiency.
The thought crossed my mind when I noticed Sasha's belly is a little bit distended outwards. But she doesn't seem to have any other signs of a deficiency that I can tell...no bowed legs, her teeth keep coming in okay. But a deficiency can exist months before there are physical signs and symptoms. I think I can reasonably assume that Sasha has a deficiency of vitamin d, considering she has no current source of it.

I guess it's something that I need to keep an eye on though. I started to give her vitamin drops today. As I mentioned in my previous post, I'd prefer she get her nutrients from natural sources but since she's not eating I don't see much other choice. I will be glad once Sasha is old enough to eat children's chewable multi-vitamins, or if she ever starts eating again.