Bill, like your wife, I am a spouse of an acoa and the main breadwinner.
"I am a wife, a mother, a nurse, which is just like being someone else's mother, and I don't know if there is a me in there"
I think what she meant is this : as a wife, mother, nurse, she is always putting another person's (you, the children, her patients) needs before her own.
She has to be strong all the time. It will be nice if once in a while, she can rely on someone else for a change ie, someone else looking after her for a change.
Perhaps, what she need most right now, is to find 'ME' time to focus on herself, do something that she enjoys away from work, work, work or family obligation so that she can find some 'balance' in her life.
It might be a good idea to also pencil in dates with your wife, so that you can enjoy time together as a 'couple'
I admit it is kind of worrying that she is looking outside her marriage for something missing in her life.