The ASHA scheme came in with the National Rural Health Mission to give every village its own health link worker. The key point is that she is a woman chosen from within the village itself, so her workplace is the village, not a clinic building.
The standard ratio is roughly one ASHA for each 1000 people in rural areas. She does home visits, promotes institutional delivery, immunisation and family planning, and guides people to the nearest facility.
The remaining choices are all formal health centres of the rural infrastructure. The sub-centre has an ANM, the PHC has a doctor, and the CHC is a referral hospital with beds. None of these is where the ASHA is posted, because her role is to stay in the community.
\[\boxed{\text{Village level}}\]