I find it odd that when I say that Olga and Tatiana were old enough to know their own minds in some of my postings, I am told that they were innocent and immature.
Then when I say that in this case, they were following their mother's lead and that they probably didn't have any input or options, I am told that they WERE mature women who wanted to do what was best and were not being pushed about by their mother.
IMHO - They were young women not children. But they were treated like children. Alexandra did not understand that they had different needs and motivations than she did and she acted like they were extensions of herself and therefore would do what she would do without question.
I am sure that Alexandra made the decision to go into nursing training and simply assumed that Olga and Tatiana would go with her without question. It might be that the young women thought it was a great idea, until they actually got into the hospital. Until then "nursing" by royals meant visiting hospitals and reading and writing letters for the wounded and contacting their families for them.
Until WWI no women of royal blood had actually entered the operating theater or assisted in surgery. Alexandra and her daughters weren't the only ones in Russia to do so. Grand Duchess Olga Alexandrovna did so and so did Grand Duchess Maria Pavlovna. But as has been posted, some women have the inclination to nurse and some do not.
Every time I am in a hospital, for whatever reason, as a patient, I always marvel at the nursing staff and how wonderful and competent they are but I know that I could not do the job they do. I would be sick.
I doubt that Alexandra ever asked either Olga or Tatiana if they wanted to go into nursing. IMHO I can see her saying, "This is what we are going to do and it will be wonderful and we will be helping our soldiers." And because the grand duchesses had simply followed her all of their lives they followed her into this as well. Had they admitted failure, I believe that Alexandra would have lectured them on duty and obligation instead of being sympathetic and realizing that they might be another way for her daughters to help.