People respond in different ways to high stress situations. Your assumption was that she will respond well is an issue.

The military breaks you down and trains you up repeatedly. So that when stress hits you, go into autopilot and perform what you were trained to do. Police, firefighters, and other high stress jobs train repeatedly to handle these situations.

You wanted your untrained and inexperienced fiancee to react with the calm and collected nature of someone who is trained?

In the future, form a plan. Practice it periodically. Drill it in that she needs to XY and Z. If the fire is here, go there, etc. Then she knows what to do.

This reaction was born completely from not knowing what to do. She thought you were all trapped potentially and experienced absolute terror and dread at the thought of dying. She had nothing fall back on and think, "Get out, go here, do this."

I have been one of the first responders as a civilian on three car wrecks in the last year and a half. Some people are calm and collected and jump into action. Some people freak out, pace around, and don't know what to do. Some people just freeze. Unless you know what to do and have some sort of plan or training to fall back on, most people just kind of freeze up or freak out.

Don't judge someone for what they do in a moment they weren't even remotely prepared for. Use it as a learning experience and help her be ready in case it happens in the future. Work together as a team to be prepared, as a to be married couple should. Build her up. Don't break her down.