That all depends on your particular problem, and person. All I can say is just relax, give them some space, try to talk things out, have some hope, and things might not work out. If they don't that's the best course.
Not having any details, all I can suggest is to keep the conversation going. Sometimes it's better to listen than to talk. Try to put yourself in her shoes and understand what she is saying. All relationships involve compromise. Sometimes, couples drift apart or grow apart. As we age, we mature and that can bring about change. Sometimes it works and sometimes it doesn't. The best you can do is to stay calm and rational, listen and then evaluate. I wish you the best.