Rescuers contemplated the safest way Wednesday to search for a woman who apparently fell into a Pennsylvania sinkhole while looking for her lost cat, saying a crumbling old coal mine was complicating efforts and endangering workers.Crews worked through the night in the Unity Township community of Marguerite to find Elizabeth Pollard, 64. A state police spokesperson said early Wednesday they were reassessing their tactics to avoid putting themselves at risk.The integrity of that mine is starting to become compromised, Trooper Steve Limani told reporters in the township near Latrobe, about 40 miles (65 kilometers) east of Pittsburgh.RELATED STORY | Cease and desist letter sent to Colorado gold mine owners after deadly malfunction trapped visitorsRescuers had been using water to break down clay and dirt to remove it from the mine, but that action was making conditions dangerous for potential other mine subsidence to take place," he said.We're probably going to have to switch gears and do a bit more complicated dig, he said.On Tuesday, they lowered a pole camera with a sensitive listening device into the hole, but it detected nothing. A camera lowered into the hole showed what could be a shoe about 30 feet (9 meters) below the surface, Limani said.It almost feels like it opened up with her standing on top of it, Limani said.Pollard's family called police at about 1 a.m. Tuesday to say she had not been seen since going out Monday evening to search for Pepper, her cat.In an interview with CBS News, Pollards son, Axel Hayes, said he is experiencing a mix of emotions.RELATED STORY | Further decline in the coal industry gives rise to a new phenomenon: Zombie minesIm upset that she hasnt been found yet, and Im really just worried about whether shes still down there, where she is down there, or she went somewhere and found somewhere safer, Hayes said. Right now, I just hope shes alive and well, that shes going to make it, that my niece still has a grandmother, that I still have a mother that I can talk to.Police said they found Pollard's car parked near Monday's Union Restaurant in Marguerite.The manhole-size opening had not been seen by hunters and restaurant workers who were in the area in the hours before Pollard's disappearance, leading rescuers to speculate the sinkhole was new.Authorities used an excavator to dig in the area, where temperatures dropped below freezing overnight.We are pretty confident we are in the right place. Were hoping there is still a void she could be in, Pleasant Valley Fire Chief John Bacha told Triblive.By late Tuesday afternoon, searchers were using access to a mine to try to find her and had dug a separate entrance out of concern that the ground around the sinkhole opening was not stable. Authorities vowed to keep searching for Pollard until she is found.Pollard lives in a small neighborhood across the street from where her car and granddaughter were located, Limani said.The young girl nodded off in the car and woke up. Grandma never came back," Limani said. The child stayed in the car until two troopers rescued her. It's not clear what happened to Pepper.Police said sinkholes are not uncommon because of subsidence from coal mining activity in the area.A team from the Pennsylvania Department of Environmental Protection, which responded to the scene, concluded the underground void is likely the result of work in the Marguerite Mine, last operated by the H.C. Frick Coke Company in 1952. The Pittsburgh coal seam is about 20 feet (6 meters) below the surface in that area.Department of Environmental Protection spokesperson Neil Shader said the states Bureau of Abandoned Mine Reclamation will examine the scene after the search is over to see if the sinkhole was indeed caused by mine subsidence.