Why did my dog stop sleeping in my bed?

My family's 12 year old toy poodle cross has suddenly stopped sleeping with me in my bed. For the last two years she has slept with me, but then my sister moved back into the house and slowly she stopped sleeping with me and instead with her. I'm very confused as even when my sister still lived at home she slept with me, and I am the person who takes care of her the most. I even give her the most affection than anyone in our household because they prefer my sisters own 2 year old toy poodle. Can anyone tell me why she all of a sudden stopped wanting to sleep with me in my bed? Nothing else has changed, and it makes me feel quite forgotten about.

Maybe she was getting to warm on your bed? If you closed your bedroom door at night with your dog in with you would she try to get out?

Has your sister moved back in due to problems? I wonder if your little dog thinks your sister needs her more at the moment.

Otherwise she is seeing you as alpha and your sister as a fellow pack member.

Maybe the dog thought 10 in a bed was a bit overcrowded :