My older grandma pooped on my 10 year old sister?

RAVENSIA WASHINGTON Asked: My older grandma pooped on my 10 year old sister?

I was supposed to be watching her but she is senile and psychotic
She has parkinsons and alzheimers and schizophrenia
She is crazy and she's done things like these before
She will do anything you tell her to though and now my sister wants to tell my parents cause she got the poop in her hair while she was sleeping and she can't get it out???
What do I do I'm scared?? What do I tell my parents cuz they'll believe my sister cuz we always pull pranks on each other but I would NEVER tell my grandma to do that!!! What do I tell my mum and dad????
Please
No joke
They're going to ground me for months and they're going to beluieve her!!
And my grandma keeps saying she doesn't remember plz