Hello Jacqueline, I'm Dr. Deb.
I recently came online and see that your question about Elsie hasn't been answered. I'm sorry that you've had to wait for a response but if you still need assistance, I'd like to help if I can.
I can imagine how disappointing and frustrating this problem must be for you, especially since she seemed to be doing so well.
I do think that some dogs are born with what I can best describe as personality disorders; they don't have to be abused or mistreated to be more wary and nervous with strangers or other dogs.
Dealing with this sort of fear and anxiety can be very difficult to change or modify but I do believe it is possible with a lot of time, a lot of patience, a lot of love and a tremendous amount of training.
In order for her to significantly change her behavior, the current negative association she has needs to be replaced with a more positive one.
Hopefully, this can be accomplished with positive reinforcement techniques and desensitization.
First, she needs to learn basic obedience commands such as sit/stay. She needs to learn them so well that the instant you give the command, she obeys it.
I would use really yummy foods such as steak or meat or small amounts of hot dogs...something that she really likes a lot. Lots and lots of praise when she does what you want.
Depending on where she's the most fearful will depend on where the next step is done...either in your home or in your back yard, etc.. But, it doesn't really matter since the principle will be the same regardless.
Enlist the aid of a friend, or neighbor...someone she doesn't know. Then you need to have her sit/stay when they ring the bell or knock on the door; she is still receiving praise and food during this exercise. When she doesn't seem to react to the bell or the knock on the door (if she reacts at all), then the door is opened, and the visitor just stands in the door with no attempt to come inside. She's sitting and being fed treats and receiving praise for ignoring the stranger.
If she immediately reacts in a negative way, then the stranger only opens the door for a few seconds before shutting it.
Eventually, the stranger comes into the house but doesn't talk to her, doesn't make eye contact with her...basically ignores her. All the while you have control over her with her sitting/staying and being fed her treats.
I think you see the pattern here.Slow, baby steps until she is comfortable with each phase before you move on to the next one. You can't rush the process. Everything is very low key; you are speaking in a firm but calm voice but you are making the training sessions fun, too.
At some point, once she seems really comfortable with them in the room, they can feed her too but only if she is in the sit/stay position.
Practice session should last about 10-15 minutes at a time, several times a day.
The same principles can be applied to strange dogs. Again, you'll need someone to work with you on this. Have her in a place where she's comfortable (such as your yard) in a sit/stay position, feeding her treats. Arrange for her to visually see this strange dog but it's not close enough for her to feel threatened.
The dog will eventually be brought closer to her, decreasing the distance by small amounts, but if she starts to react negatively, they should immediately turn and walk away. You'll be able to quickly tell when she's comfortable before bringing the dog closer to her at each phase of the training sessions.
The goal, of course, is to have this other dog sitting next to her with no reaction from her at all.
Hopefully, you'll get her to the point where she can be walked to the park but when she's to meet another dog, she should be sitting being fed treats and receiving lots of treats.
Other helpful tips:
Elsie must earn everything...the basic principal of "nothing in life is free". She sits/stays before she is fed, she sits before she goes through a door, she sits before her leash is put on for a walk, etc. Initially, I would reward her with a treat every time she obeys you, then I would intermittently reward her (sometimes she gets a treat but other times she doesn't) and eventually she is rarely rewarded with food.
Everyone that Elsie comes in contact with (especially your family) should make her obey commands before they pet her , before they give her treats, etc.
Obviously, this will take a great deal of time, work and patience but I do believe that you can change her reactions/behaviors. She needs to build up self-confidence and trust and she should be young enough to do so.
I hope this helps. Again, my apologies for the delayed response. Deb