How old were the girls when you got them? If you know they were P.O.L. (point of laying) when you bought them, they should have another year or two of productivity before it starts dropping to the point that a commercial farm would get rid of their chickens (usually a production red or some type bred for egg-laying) (18 months to 2 years). If you don't know the age, just bought them as laying hens, they may already be older, may have been culled from someone's flock for non-production, may be slacking off due to the season. You can do a search for Henderson's Chicken Chart on this forum, look up your breeds and learn about their expected laying careers. If you decide to get all new birds, you may be able to find a new home for your one good leghorn, where she wouldn't be a problem for you with new birds. Chickens don't want to be solitary; they are social critters. Good luck. I bet you make a wicked-good barbeque chicken!