A.M.
Your 6 year old knows about the potty. She is just acting out due to the fear and lack of attention she has been getting with the little one being sick/at the hospital. Have you talked to her about why you went to the hospital? That it is getting better? Tell her how good and what a big girl helper she has been while her sister was sick??? We have no idea how kids process stresses that we have. She may still be worried about her sister getting sick again, she may think she is next to get sick, she may think you will leave her to take care of her sister and forget about her... lots of stress for her. A new baby is bad enough to get used to for a little 4 yr old who is used to ALL of her parents attention, but a sick baby would be too much for her to process. I am sure she is just scared/sad that she is not getting attention like she used to and that she doesnt understand all the hospital stuff... talk to her about it!!!