We don’t know she was a rescue henNeed situation?? Is it a broody hen? How long she been sitting/ broody? Where is she located? (in a private fenced area from other chickens or in high up nest box or outside in an unprotected location?)
If she's broody and in a safe location and your ready and prepared for chicks, then go for it! .. Slip them under her at night if you like or when she's off the nest for a break you can put them in. Or just lift her up and put them under her -just depends on her behavior. With my chickens I just set the nest and they sit. What breed is your broody?