Farm Legal Advice: I'm worried my elderly father's girlfriend will take the farm

My father is in his late seventies and has allowed a woman to move in with him... will it affect my inheritance?

If a couple lives together for five years or more, a partner may acquire rights to each other's property.

Dear Karen, 

My father is in his late seventies, and he has 100 acres and the family home. He is retired from farming now, and the land is rented to a neighbour.