Hi akmarad. At least the thing going for you is that you got a diagnosis that her Ca and D are low.
My pullet was a BPR so she was bigger than Betty (6 lb). On Oct 8 I gave her 0.25 cc of the A+D which was 6,600 IU/kg bw or 17,500 IU total IM. My notes: Seemed better the next couple days then developed diarrhea. I don't remember the diarrhea being as bad as what you describe and she certainly didn't get worse. On Oct 10 and 11 I gave her Poultry Cell and noted she developed diarrhea on the 12th (meaning in between her diarrhea cleared up). I gave another same dose of A+D on Nov 9. I did not note any adverse reactions.
In looking at my notes, I also treated a 5 lb hen. I gave her 0.15 cc at a rate of 5,000 IU/kg bw which was a dosage of 11,250 IU IM. I did all the same things and also gave her a Manganese tablet. She never had any adverse reactions that I noted.
Because Vit D is fat soluble I was nervous to continue frequently at very high rates without direction from a vet. I ordered the Osteo Form which has Vit D and phosphorous, reasoning that the ratios should be balanced for long-term use. I really like the product! I've been top dressing the feed of a couple birds with that and you would not know they ever had a problem. Have you researched calcium tetany?? This is my latest theory. Around the time this all started (April/May) I had switched feeds to a local mill. I thought their formulation must be off so I started supplementing with vitamins and minerals all my birds. My birds are all in top shape and look amazing (for example I've had eggs coming out of my ears all winter) so it was really odd to me that a couple birds would have this problem all of a sudden. In addition, they never stopped laying. In fact they were some of my best layers. Around this time I noticed a strong smell and some difference in quality from the oyster shell. I asked the feed store twice and they shrugged it off. At any rate, in reading about calcium tetany, I think these couple of high producing birds (the pullet grew super fast as well) had a calcium deficiency. All that to say, of all the things I did I think the Osteo Form was the best solution. I've also switched to a different oyster shell source.
I hope Betty improves. As you know, Ca strengthens muscle contractions so your theory may be correct. I certainly don't think you gave her too much vitamin D but it is possible it, or the Ca, triggered GI upset.
