It could be a number of problems. She could have a unirary infection of some sort, and marking the bed is trying to tell you something's wrong! It could also be dominance, try not to allow her on furniture or the bed and start NILIF, it's probably somehow related to maternal instinct. Have a vet check her out at her next litter check-up (if she still has the litter?), until then close your bedroom door

Also, a litter "calming down" females is a myth. Only maturity, training, and exercise can truly calm a young dog down. Spaying your dog (of course once her litter is weaned and sold) will help 100% with marking behaviors of intact females, and also prevent many health problems.