Meri is your sister who you only have as family since the rest was murdered after you left to get some wood. But a curse was bestowed on her making her have no recollection of what happened and that she possibly killed them? Or maybe not.

Ever since you carry your sister often in a wooden box on your back to keep her safe and sound. It's hard for her to communicate but she makes perfect notions or hums to indicate things rarely able to say anything really.

She preffers her smaller form to show she feels safe, content and it's not only just that but also stealthy as heck.