Housebroken dog peeing on our bed - HELP

We have a 5 year old beagle that we got when she was about 2 from a shelter. She is housebroken and usually sleeps with our daughter. A few months ago when my daughter left her room for a few minutes before going to sleep, the dog peed on her bed. She has now done this 3 times. Today we got home from work and there was pee on our bed! What would inspire that behavior?? She has had no accidents anywhere else in the house so it seems there must be some messege somewhere. We have just added a young sheltie into the mix and this happened after he came along but I can't see a conneciton there. They get along very well and it has been 6 months. He is also house trained.

Oh sure there is.

Your dog is marking you and your daughter as hers since the newcomer has arrived. She is marking an area that is the strongest of your scent in the house, and one that is charged with meaning in the dog world. Your sleeping area.

Close the doors to the bedrooms for now while you are gone.

Yep, she is marking her territory. You may have to start crating her or keeping your doors shut when not supervised. she loves ya'/

ahhhh

Thanks to both of you for your responses. I was hoping it was something like that but had no idea it might be related to the new edition 6 months later. You won't be surprised to know that Neo slept in our room a few nights this week. It seems to explain why she did our bed this time.