How can I convince my sister to wait? PLEASE HELP!?

Okay, my younger sister is a sopre in college. She has always been a little impulsive, but this is really worrying me. Her fiance dumped her this morning (he told her that he had fallen out of love with her and never wants to get back together) so she is obviously distraught. Before they met, she was talking about joining the military but decided against it when she fell in love with him. Now she is meeting with a recruiter today and planning on enlisting tomorrow! WHat can I do? She is making this decision based on the breakup and I know it. I love her so much and just want to protect her. If she wants to join, that is her decision, but what can I say to try to get her to wait until she calms down some. I know she is upset beyond words. Not only did he dump her, but they have to mess with dividing up things they have bought together and their pets and she has to move out of his house. I know this sounds all over the place but I am just worried for her. Is there anyway of getting her to wait a little bit first. I think she needs to deal with her emotions on this before she makes life altering decisions. Please help me. I am so worried.