Is she an adult? I understand spouses being sad if a partner doesn’t spend enough time with them. Or kids.

But sister? And crying? Is she getting any type of help? Therapy? I love my brother dearly and sometimes do wish we had more time together but I certainly wouldn’t be crying let alone complaining.

She needs her own therapy. You aren’t under obligation to discuss her issues in your therapy or spend any particular amount of time with her. It’s highly unusual