Does she want a friend?
If she's blind, does she have her own space/coop where the food/water is in the same place all the time. Sometimes if a hen with a disability is managing well on their own, in their own space, adding another bird whether a chick or adult can cause undue stress on the hen and her peaceful environment.
It's like moving in and unwanted guest.
A chick will grow up to be an adult, they may get along or the chick may grow to become a bully, it can be hard to know.
If the chick becomes a problem, then you'd have to think about rehoming or adding a lone bird to an existing flock which can also bring on undue stress.
To me, if your hen is thriving by herself, then I'd leave her as is to continue on living the best she can.