im sorry for your loss, i lost my syrian a month ago she was 2 and a half years old called Nibbles, i too cried a lot after she passed i feel like they are 100% part of the family i treat all my pets like they're my children. i honestly dont think your other hammy is missing the one that passed. there could be something else going on. she could just be cold and want to stay in bed or she could be getting old and have less energy to go exploring. i would recommend doing a health check when you get a chance to make sure she's still looking well (not hurt her legs at all limiting movement, no lumps or bumps, no overgrown teeth causing pain...) if she's eating and drinking i wouldnt worry to much about it. if it does start concerning you then you could book an appointment at your local vets for a checkup to make sure all is well