How do I stop my sister from going to Shincheonji?

 Almost a year ago, my sister was invited by her friends to join a Bible study group and she later invited me. I was a bit hesitant to attend but I later went to a meeting. I didn't see anything suspicious at first because everyone seemed pretty nice but some of her friends made me uncomfortable. I still attended meetings and I got to the "intermediate" stage of the study. But the people there still made me uncomfortable because even though they were nice, it felt like they were constantly guilt-tripping me to attend.

There were even times when my teacher embarrassed me in front of the entire class because I forgot my Bible sometimes. They also didn't allow people to think critically about their teachings. I finally told them I decided to leave because my class schedule was not compatible with the study group's time and the teacher tried to manipulate me by saying that my leaving isn't what God wants and that leaving their Bible study was bad for my spiritual life. I told him I was also leaving because of his passive-aggressive attitude. I left and never got to the Revelation stage of the study group.

Right now, my sister is currently teaching in the same Bible study group, and ever since she started teaching in the Bible study group she almost NEVER leaves our room EVERY DAY. Sometimes she won't even eat breakfast because all her time is focused on the study. After I left, I didn't trust any of her friends from Bible study because of my experiences but I never associated the study group with cults.

The biggest red flag was when my sister kept on calling these local news stations and she mentioned that her friend has a tip from someone involved in Shincheonji about how the South Korean government was blaming this church for the rise in COVID cases and that the church is innocent. My sister also called local news stations telling them about how recovered members of Shincheonji donated their plasma. Since it was my first time hearing about Shincheonji, I looked them up and that's how I found out they're a cult and that a lot of their teachings were what was taught to us in Bible study. I told her that I found out that there were rumors that Shincheonji was actually a cult and she got super defensive and told me I was just assuming.

Even though the Bible study group is not named Shincheonji, I think they're 100% involved with the cult. She's even putting her health at risk for the "sealed" Word. She won't eat 3 meals a day just so she can attend their seminars which start at 8 am. My problem is how do I convince her to leave and how do I cut off this Bible study group from our lives? It's definitely affecting my sister's personal life.