Hello,
Your sister will benefit from seeing a clinical psychologist or psychotherapist. Talking about our struggles and difficulties to a professional and getting appropriate assistance can help her in finding her way. People who are undergoing difficult life circumstances are often deeply affected with a myriad of feelings such as guilt, regret, shame etc impacting them. You can try talking to her about what’s bothering her, and try to understand empathetically how she is feeling currently. Life transitions such as separation can be tough and demanding. A little help can go a long way.
Next Steps
Consult one in your city, or here through practo.