I have two responses:
Fractured elbows can be notoriously prone to stiffness. The nature of the joint is that the two bone ends are very "congruent" meaning that the two are tightly shaped and in close contact (as a tight fitting glove as a metaphor) - this means that if there is a disruption of the surfaces there often can be problems with the movement between the surfaces hence a lot of stiffness. It isn't possible to give specific advice as I don't know the exact nature of the fracture. Pain is also a common problem when trying to improve the range of motion. However there could be other complications. For example it may be that there is some involvement of the nerve complex (known as adverse neural tension) and this can cause a lot of pain and may need examining. You described getting the pain in the forearm when the therapist moved the shoulder and this could indicate such a problem.
My second response is more about the way the therapist communicated to you. It is clear there is no empathy there. In my experience having someone who can build rapport with you is essential for the smooth progression of your rehabilitation. For example if a procedure is particularly painful being understood with a sympathetic ear and having some problem solving for dealing with the pain is really important. It may be necessary (and by the way I don't know this) to have the joint moved in such a painful way but there are such things as pain management options. All in all if the therapist behaved the way you said - well it wasn't very professional and I don't think you were treated with dignity and respect that you should be accorded with.
The best answer is to may be seek help from another therapist whom you can have a good working relationship with. you may also need more of a team approach - perhaps a physician could help with the pain management side of things. Whatever, it is true that you do only have a limited window of opportunity to get things moving so I would persist with help now.
I wish you well with our recovery.