She could be busy, she could be having a tough time dealing with whatever happened between them, or she could be going through something else entirely - whatever the case - I don’t think any of those things have anything to do with her CLEAR refusal to discuss things with someone she CHOSE to be in relationship with for two years.
How difficult is it to EXPLAIN what is going on. Nothing happening to her right now is happening without her knowledge and consent. She’s not a prisoner somewhere, having silence forced upon her. The fact that she has the freedom and the ability to give your brother a real explanation and is choosing not to, is disturbing.
It sounds like she’s through with him, and has moved on, but is keeping him around just in case her secret plans aren’t everything she expected they would be.
Her behaviour is unacceptable and ridiculous. If you can’t GET OVER something that happened, then explain that. Hey, I’m not big enough to get past our disagreement, or hey, I don’t feel like it would be beneficial to my life to bother trying to work things out with you. She could have said something. Something more