Ooh , that's a danger in itself, sorry , fire person talking here:)
What you may need to do is walk her from the front of the house rather than to try and get her through the back door. For now unless she knows and obeys her commands very well, she will continue to put on the breaks, especially since it is too soon after the fireworks. If she is well trained to heel ,sit, down, etc. then I would start having her do these commands on lead while in the house, and not at a time she needs to go out for potty. Praise her well for every command she obeys on the first asking, use hot dog sliver or chicken slivers. A few times walk her out the front door to the street curb to do her business. gradually as you work her over time inside the home on lead with commands you may be able to heel her right out the back door.
If there is a toy that might motivate her if you throw it out the door then use that as well/.
What I fear may happen if you just put the lead on her to tempt her out the back door that she will soon associate the lead with something bad , unpleasant , or frightening and we don't want this to happen.
It may take some time before she will go to that area again but do not coddle her or sweet talk her or she will feel there is something to fear if she crosses that line. I would not even tempt her at this time by tossing treats out the door because she is wise to that event as well. So get her practicing inside on lead for commands, as she is doing commands you can throw in a trick or play here and there to lighten things up, and gradually when she seems at ease with inside training and she believes she will be taken out the front door, then you heel her and run her out the back door instead.
Anytime we baby a dog when they are frightened it increases their fear. Right now she knows the lead means she may have to go out that back door and we want to change that thought process and try again at a later time when she is not sure where you will be taking her.
If there were a gate in the yard I would say lead her in through there for now and then try to get her to go through the back door that way as that is also a different way to associate the back door.
I am careing for a neighbors dog so I will be stepping out for a few minutes , but will check to see if you have any questions when I return.
ah one more thing, if you do not clicker train I might suggest that as a positive reinforcement thing.
Clicker training/positive method training
video’s to see how clicker training is done, scroll down to videos http://www.clickertrainusa.com/clicker-training-videos.htm