Not her parent but concerned

Ra

To start off, I’m a nanny for an 11 month old. I’ve been with this family since she was 6 weeks old so it’s been a nice little chunk of time. The baby has a 5yr old older sister. I’ve noticed a change in behavior in the older sister and I’m not quite sure what to do. I’ve spoken to her mom about it and idk if I need to try again or what. She’s always been a sensitive kiddo, but lately, she cries about literally everything. And she randomly gets super mad but calms back down in seconds. Their parents are on vacation and I’m staying in their home with the baby, and the older sister spends the day with me, but the evenings and nights with her grandparents. And she just sobbed that she doesn’t want to go to her grandmas. My SO says I need to mind my own business and do my job and that’s it but the older sister is only 5. I’m concerned with what’s going on. She became an older sister, started school, her dad started a new job with new hours, so I’m thinking it’s the change of schedule but idk how to get her to go back to being a happy kiddo. Idk. Advice?