From the Super Mario Wiki
Queen Mushroomkhamen appears to be the guardian of her tomb, where she and her son Prince Mushroomkhamen rest in mummy cases. Apparently, she will awaken if anyone enters the tomb, and will pursue any potential thieves.
When Hip and Hop Koopa heist Prince Mushroomkhamen's mummy case from the tomb, Queen Mushroomkhamen awakes and chases after them, although she is unsuccessful in retrieving the case from them. Outraged at the loss of her son, she goes on a rampage through a local bazaar, scaring everyone out of the place.
When Mario, Luigi, Princess Toadstool, and Toad arrive to stop Queen Mushroomkhamen, she winds up mistaking Mario for her son, due to the fact that Mario bears a huge resemblance to him. Mario tries to get away from her, but she ends up catching him and brings him back to her tomb.
Queen Mushroomkhamen refuses to listen to Mario babble on about how he is not her son, wraps his body in bandages, and forces him to take a nap in her mummy case. Eventually, Queen Mushroomkhamen falls asleep, giving Mario a chance to escape from the tomb. However, Mario's getaway awakes the queen, who breaks out of the wall of the pyramid to chase after him.
Mario is then saved by his friends, who have successfully retrieved Prince Mushroomkhamen's mummy case from Castle Koopa. With her son back, Queen Mushroomkhamen scolds Mario, but is quickly sidetracked by Luigi, whom she mistakes for her husband. Not wanting to suffer the same fate as Mario, Luigi runs off as she chases after him.