After I posted, I looked up chromium. It is sometimes given as a supplement for diabetics. I have big babies, but they run in my family, so it is not an issue of diabetes. thus, chromium wouldn't do any good for someone with babies who are just big due to genetics.
Is diabetes/blood sugar issues the reason for your big babies?
Would she (Would you) be willing to birth a breech baby? If no is the answer to both, I wouldn't mess with a supplement like chromium... If the answers are yes, it'd be a judgement call.
What about going to chiro for help with turning a breech baby, ordering the hypnobirthing cd for turning a breech or doing techniques on spinningbabies.com?
In what little I read, (I am in no way an expert considering I knew nothing of chromium prior to reading your post) I see that the effects of chromium prenatally in humans are unknown...That lab mice show some harmful effects... I also read that one must be careful when choosing a supplement for chromium, making sure it is in whole food.
That's all the input that I have for now... Still processing... 
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