UAL747DEN,
Appropriate comment from the other posters, to add to them....
There are many symptoms of hypoxia, feeling sick, or extremely sick, as you put it, is not one of them. Headache? Maybe, during the hypoxic state, but severe, and after the possibly hypoxic condition, very unlikely.
If her symptoms continue, my suggestion is for her to seek medical advice, it appears to me that the circumstances of the flight were not the cause of her problems.
I hope that she recovers quickly.
Regards,
Old Smokey