CoCo started doing this too soon after I got her (she was 8 months old then). Mind you, CoCo hardly EVER has accidents in the house. She is 99% right on when it comes to the potty pads. She and Muffin slept with me but CoCo is very possessive of me and she started 'claiming' me by wetting the bed. It was as if she was marking her territory. I learned this from the vet and he told me to NOT let her sleep with me. So for 6 months neither of them slept with me and then about a month ago I thought that she had learned her lesson. I put them both back in the bed and all was well for the first two nights and then, don't you know it- she started peeing in the bed again!
I was so angry at her but I know her little personality and she is just Miss Possessive and she couldn't stand Muffin being in the bed too. She always wants to claim me for herself. So needless to say, she is NOT sleeping with me anymore. Every once in a while Muffin wants up in the bed with me and I will allow her but not CoCo. So I have two doggie beds on the floor next to my bed and that's where the girls sleep. They are close to me but not in 'potty shot'!