A lot of people have a hard time with the RE part of FIRE. You might do better just focusing on the FI part (control, flexibility, freedom) and leave the RE part out there just as a possibility you may decide to do at some point if the time is right.
I'm not too much into pessimism and scare tactics, but she might need a little dose of reality before it really sinks in. Not having worked full time in a career type job, your girlfriend probably has no clue what it is really like. Right now, in her mind, the job that she has worked so hard for in school will be awesome, and if it isn't, she'll just find another one. Maybe, but maybe not. A few years in the working world will almost surely change her perspective.
She was probably in her early teens when the last economic down cycle came around, maybe too young for it to make an impression, especially if her parents were not affected.
Growing up, both my parents worked in the public sector and there was NEVER even speak of a layoff or relocation. Layoff/relocation announcements in the news meant absolutely NOTHING to me until around 4 years into my first job when the small family like business I worked for was sold to a larger company. I still remember when my first coworker was laid off. This was 2007, right before everything tanked, it was a terrible time to get laid off. I was shocked into reality by the experience. The reality was, that at any time, your world could get turned upside down by events totally out of your control, all you can do is be prepared. At the time, I was still a long ways off from FI, but in the event I had been laid off, unemployment would have easily covered most of our expenses, as well as having a decent stache to dip into if needed. Over the next few years, my wife was laid off 3 times, yet financially, it was barely a hiccup as we did not depend on her income at all.
This is a fragile time, get it right, and you have a huge jumpstart on your financial life. Get it wrong, and you might be towing around that boat anchor for a long time.
This is what I tell people just starting out:
You may love your job now, but 5 years down the road you may not. Save money to give yourself flexibility if that time comes.
When a recession, merger, acquisition, restructure, etc. comes around, people (even the good ones) lose their jobs. Recent hires are often the first to go. Be ready. Don't box yourself in with high expenses thinking the gravy train will go on forever, because many times, it doesn't.
If kids are in the picture, your are going want every bit of financial flexibility you can possibly get.
Good luck!