It's difficult to know what really happened, and also not to impose our 21st century sensibilities on the matter.
I, too, have read that she suffered a breakdown of sorts while working alongside her mother and sister in the hospital, and that she was found in a linen closet vomiting into a towel. Given the disturbing situations that would be part of hospital work, plus Olga's particularly sensitive nature, this almost sounds predictable. From what I remember reading, after that episode she was given a desk job.
Her mother writes about Olga's "sulks" and so forth. I rather think it was a combination of Olga's age (and being expected to be both a role model to her siblings, plus a longterm "child" to her mother), personality, the ongoing situation of war, the absence of her father, the omnipresence of her mother, and some thwarted romances. Good golly, who among us would not be moody and depressed if we had to deal with all of that!