Destiny, I think you are fired. I do not think you can act fast enough or do anything that will stop this from happening. Do not sign anything. If you did not do anything illegal, do not ever admit that you did or sign anything saying you agree to their perception of the incident. Do not let them talk you into resigning to avoid being fired. Being fired is always for the best, due to the fact than when you are fired, it was the employer's choice to fire you, not your choice to quit. Agreeing to quit tends to make you look guilty of whatever they are accusing you of.
I am not at all sure you will have any recourse related to ADA. I am not sure how COBRA insurance will tie into this, or if they have to pay out your sick leave days. More knowledgeable people on this site can assist you with these issues. Since this was not an on the job injury, I do not believe that you will have any Worker's Comp eligibility. Did the doctor release you to return to work with the sling on your hand? Did you have a doctor's statement to give to your employer, saying that you were able to return to work?
If you receive the official word that you are fired, you should receive something saying the actual reason for your termination. You should immediately file for unemployment insurance and begin this process. Filing for unemployment may be your only recourse in this situation. In any case, it should be the first thing you do if terminated. It will, if nothing else, clarify the issues surrounding your termination.
The wages you have made in the last year and a half will probably be on record to set up a claim. You will be asked exactly why you were told you were fired. It is important that you specify only the last issue. An employer cannot keep you from being approved for benefits by saying five or six different reasons, such as (1) she was out of work last year for a while (2) we found some problems with her work and put her on an improvement plan (and incidentally, was there a time limit on this plan, and were you later told you had improved or given any feedback?) then (3) we had problems with her attendance and then (4) she was tardy and we gave her a warning and then (5) we think she stole something, or changed some deposits and (6) she was working while her arm was in a splint and that's not approved.
See, that's six different reasons, none of which was documented and followed up to the actual event of your termination. If you were out of work this last time with a doctor's excuse due to your injury, you should have that doctor's excuse available in case they go for absenteeism.
You will file your claim, and tell them exactly what was said to you as the reason for your termination. The day you were actually told you were fired.
Do not bring in all these other issues. The employer will be contacted, and they probably will provide a whole laundry list.
If they have actual excellent proof you were stealing, such as you on video, or very significant records of fraud in your handwriting or on your accounts, then you will not win unemployment and probably will not have any kind of case against these people. Having an injury does not protect you in any way if you were fired for a genuine good misconduct reason.
But I would definitely file for unemployment immediately, so you can determine exactly what they are going to say is the reason they have terminated you and what documentation and proof they have of this. It costs nothing, and if they are really as disorganized in their reasons for termination as it sounds in this post, you may be approved for benefits.
Then I might retain an attorney to assist you with your unemployment appeal if the initial claim is denied or if it is approved and your employer appeals, which I am very sure they will do. You may very want to discuss with this attorney the injury and the work termination issues related to this. If you qualify, legal services in your area will help you.
By the way, tell us what state you are in. Also, please stop and start your sentences with a period and capital letters or put spaces in somewhere so it is more easily readable.