My 8 year old told her 16 year old sister that she hates her

So my daughter, 16, got a job as a dance instructor for a dance team made up of kids age 6-11. She would spend half of her day at the dance studio with the children. My 8 year old daughter has been upset with her sister because of all the time she's been spending with the other children. When she first started they referred to her as "Ms Cordova" but now they either call her by her first name or "big sis." She requested that they cut back on days spent together due to coronavirus and has continued their dance lessons over Skype with parental approval. My younger daughter asks her if she wants to do things with her like watch a movie and her sister will say no sorry I'm busy. Today my 8 year old got upset when her sister declined her again and told her that she hates her and wish they weren't related. Then she ran off to her room. Her sister started to run after her but I told her I think it's best if she's left alone for now and to let me talk to her first. I spoke to my 8 year old and she told me that her sister has replaced her with new baby siblings. I tried to tell her that's not true at all but she just wasn't budging. I don't know what to do.