"She was a long time in getting over her illness" sounds like another old English kind of sentence. Writers do take liberties sometimes in books, maybe even starting new ways of saying something. But this sounds like an old phrase.
nekocat san, I'd like to thank you for your posts, they are very interesting and I'm also learning from them.
It seems that you need to make your post a certain length, otherwise the programme "compalins" your message is too short regardless it is written in Japanese or English.
And may I suggest something? It would be nice if you could add a little translation to your Japanese message, because not all the members answering your questions are learning/understand Japanese, it's a pity they cannot understand what you are saying, especially when it is your words of gratitude for them.
It seems to me to be a small thing but it would be more correct to say
"She was a long time getting over her illness" as apposed to
She was a long time in getting over her illness.