Neighbor is walking in hallways to asks for food knocking on neighbors doors, but does not admit she need help at home.

I would say there is some Dementia going on here. Have you notified the landlord, maybe they have contact information. If not, ask that they call APS telling them he has a vulnerable elderly tenant and what she has been doing and seems not to be able to care for herself.

It's not a case of admitting or not admitting, as it sounds like maybe she has anosognosia. It's a feature of many disorders, and it means that they can't tell there is something wrong as their brain is affected in the areas that would allow them to see the problems. Yes, report this to APS, more than once if necessary. She needs help.

What a good thing it is that she has you for a neighbor and that you care enough to try to help her.

Yes, call APS. If they do not respond, you can call 911 and ask for a welfare check. It's thoughtful of you to care.

Call her family if you know who they are. If not, call APS to report a vulnerable and hungry elder living alone.