My sister lives in Creedmoor, North Carolina and is in need of home repairs but can't afford the cost of repairs. Is there an agency that can help her. She was the primary provider for my Mom before she died and I would like to see her have some needed repairs to her home (new windows, carpet, flooring in her kitchen, etc.).

Rarely do any local or state agencies provide for home repair. There are just too many people with no home at all. Sometimes local charities and churches will help with labor.
Is there are reason that her siblings (you, any others) aren't helping, given that she (I presume) didn't get paid for all the care she gave to your mother? Or did she get your mother's house?
She could get a reverse mortgage if she is 62+. She could talk to her town about defaulting on her property taxes. They will accrue at high interest, but often the town will just let an older owner go, as long as the debt isn't greater than the value of the house.
I would look into the reverse mortgage - the lender pays her monthly and gets the house when she dies, and pays any heirs the balance. If she lives too long, of course, they can kick her out when they have paid enough years of payments.

Aren't you able to provide any help to your sister?

The Methodist church for one that I know of, does many repairs throughout the U.S. I know of cases where they have put on a new roof. Don't know about windows.
Much of the work is done during summer months by students, but some Meth. churches and most likely other denominations have a year round program(s).
Suggest that you make some calls and find if any help is available at churches, etc in your area.
Is your sister a senior citizen? If so, you may get some suggestions from an Office on Aging type facility in your county also.

Does not sound like she is elderly, most community help is for the elderly.

She can check with her local religious group. Of her choice. Often local churches, where you are a member, are helpful.

Methodist, Catholic, and Lutherans have charities group that help,

If she is veteran, some of their groups help.