So the question is really how much do you need her? If you need her to improve or to diversify, even if she lays only 10 eggs next year (which is probably way low), those 10 might be the key to moving your own line along to the next step.
From an economic perspective, you're not going to make money on any of the chickens you have unless you can sell chicks for $10 each and eggs for $30 a dozen until you don't have any more. How much will it cost you to keep one hen? Maybe $30-50 for a year maybe less, maybe more depending on free-ranging and types of feed you use. If I need one of my hens or she is special to my breeding program, she isn't going anywhere even if she's 20. If I get 5 fertile eggs a year and one of those turns into the male or female I need, I figure it was well worth it.