Not sure why I put her age - its not really relevant, but I wouldn't want to give her anything with explicit sex scenes or excessive bad language (she's not a prude though and can handle a bit of swearing)
She's very with it mentally, used to be a scientist so enjoys scientific themes, likes strong women characters, like a bit of humour -- books I've given her recently which she's enjoyed have been Remarkable Creatures by Tracey Chevalier, Solar by Ian McKewen, and Deaf Sentence by David Lodge, she enjoyed Mark Haddons Curious Incident too.
I'd prefer to avoid anything that deals with widowhood, losing your spouse or dementia, as we lost my Dad a few months ago.