Pol Lt Watcharapong Tienprathom said Ratree Plienkarn, 46, who works as housekeeper of the eight-storey block, noticed an unpleasant smell coming from a room on the first floor.
She and a security guard went to the room and found a dead body. She then called police.
When police arrived they found the body of Nitchaprapa Chotenakorn, 64, lying on a bed at the back of the room.
Pol Lt Watcharapong said it appeared the woman had died of illness about three days earlier.
Her daughter Hansa, aged between 30 and 35, was sitting quietly beside her mother's body. The daughter is mute and has Alzheimer's disease.
Police were contacting other relatives to formally identify the body.