Was your relationship with her OK overall before this? If you think you could have a conversation with your sister, and you had a good relationship with her, then maybe you should ask her what is going on. She may appreciate it to know that you care. If she doesn’t want to open up, then she will let you know, whether it is about university or being LGBTQ or whatever reason, but at least she would know you care and she may open up later. My sister and I don’t have a typical sibling relationship. She abused me all my life and I try to have as little as possible with her. In our case, we cannot have a normal conversation as I am in a fight or flight (more flight than fight) mode and she thinks she is my boss. Hopefully yours is better and you can tell her you care.