Sometimes you can fight fire with fire, so to speak. Nightmares at this age are partly due to the fact that the child's imagination is developing, and you may be able to use that new spark of imagination to extinguish some of those nightmares...
My daughter went through a period of nightmares at around the same age (and she wasn't a stellar sleeper to begin with, so I still remember how exhausting that was). I don't have a perfect solution, but here's what ultimately worked for us:
First, I think it's important to reiterate that dreams are "just your imagination" while acknowledging that they certainly can seem very real.
Second, give her power.
One way to do this is to help her make the scary thing into a silly thing. With my daughter it was a monster who was chasing her. So I asked her why the monster might be chasing her. She said the monster wanted to eat her. I said, "how do you know? did you ask him? maybe he's chasing you because he wants to invite you to his birthday party. Maybe he is very sad, because everyone runs away from him even though he is a very nice monster." Etc.
Another way is to explain that dreaming can be like drawing a picture, if she wants to change something, she can do it. She can make the monster disappear or turn it into a rabbit, etc. I found that the "Harold and the Purple Crayon" books were very helpful in conveying this concept.
In your case, maybe you could help her to imagine ways to get rid of or cope with the fire and the man. After you acknowledge that what she imagines must be very scary (and, yes, fire can be dangerous), remind her that fire can also be very useful and very pretty. Maybe the fire is a campfire, and the next time she sees it, she should remember to bring some marshmellows? Or, if she wants to put it out, she might need some water...maybe she can call the water fairies (or whatever), or she can use a magic wand that puts out fires. If "the man" is scaring her she should tell him to go away. Tell her that it's her dream, and everyone has to do what you tell them in your dreams. Maybe the man is very afraid of dogs, so she should bring a big dog along in her dream (unless she is also scared of dogs, of course).
Also, acknowledge that you had bad dreams too when you were little, (though I don't recommend going into details, which might give her new ideas for nightmares), but that this is what worked for you.
You can also help her to imagine happy things while she is trying to fall back to sleep. I told my daughter about how when I was a little girl I saw an episode of Sesame Street where Ernie was having bad dreams, so he imagined hundreds of ballons and ice cream cones floating down from the ceiling...I told her that I tried Ernie's trick when I was just her age and that it worked for me.
It was very reassuring and important to her that I understood what she was talking about, and that I seemed to know how to "fix" the problem (even though I was obviously winging it).
Also tell her that if she does have a bad dream, you will come to her right away. (if she thinks you might not come, it could create more sleep anxiety). But when you get there don't let it be a big drama. If she needs to talk about the dream, listen to her, but don't have a whole conversation. Try stroking her back, her hair, and reminding her that's it's not real, it's just a dream, and then help her think of happy images (puppies, birthday parties, an upcoming holiday). Once she's calm, tell her that you are going back to bed, but that you will check on her in five minutes. If she's still awake, repeat. Give her another five minutes, then ten. But if you stay until she's fully asleep, you're right, she won't have learned to soothe herself.
I still remember listening to my daughter chanting to herself, "It's not real, it's just my 'magination, it's not real.." And a couple of years later, when were on the Haunted House ride at Disney World, "It's not real, it's just animatronics, it's not real..." She insisted on going on that ride three times. So the technique seemed to work for her to some extent, and she extrapolated on it to conquer other problems/fears (not sure how she knew about animatronics). But hope this helps a little. Best luck!