In my area, All-flock is cheaper than Layer feed. So with a bag of oystershell, it is cheaper to feed the All-Flock over the long term. My guinney hens eat All-Flock and scratch mix, they are not supposed to have Layer at all - too much calcium for them. So feeding all-flock to the chickens is a no-brainer for me. Having only one chicken, go ahead and buy the bag of Layer mash, it probably takes quite a while for a single chicken to eat a bag of feed. Hopefully she is laying for you before too long.
I hope you can get some hens to keep your current chicken company. Chicken math is great!
Did you get rid of all the cockerals?