Not at all sure that a personal injury lawyer would be your best choice here. Shop attorneys, do your homework, don't try to take the easy way out by "oh, a friend of mine knows this person..." Will they, if they think you have a solid case and no money, take the case on a contingency basis? That's a good sign. Big fee upfront? Not a good sign.
It drives me nuts when the "tv attorneys" in my area advertise that "It's a proven fact that people who have attorneys collect more $$$ than people who do not!" Heck yeah, because they only accept the cases in which people stand a possibility of getting money. Or those of people who pay them a substantial cash retainer if your chances aren't that good.
So wait, see if the situation upscales. Be sure you are not the one who keeps it going. They've had you in, they've threatened you. Wait and see if they're going to do anything else about what they've threatened. And while still working, and getting the perks of the job, like the people who genuinely appreciate your services, and the money you're being paid, do some quiet research about who might be a good labor issues attorney for you. You haven't had a "personal injury" like in a car wreck or something. You're having a labor issue.
Another word, friend to friend here, keep-a the big mouth shut! DO NOT use your co workers, or even, to some extent, your friends and family as your sounding board, worry aloud or talk about how you've been treated and what you are going to do or have done about it. The more you feed things, the bigger they get.
DO NOT discuss your situation or what management might do with ANY of your co workers or anyone who knows any of your co workers, etc. That's the surest way in the world to keep the situation escalating.
I know you have had a hard time and you see a lot of potential bad things happening, but really, "She spends too much time telling her personal problems to others on the job" is NOT something you need to have said about your work when you are doing a good job and you know it.
You're an army of one, be on your own side instead of rolling over and hoping others will treat you okay because you've had a very hard time and you're a very nice person. You are a nice person, this is true, but you know from reading here that employers aren't required to be nice or to like you or to treat you fairly, and many times they do not.
In fact, life usually doesn't do this for us, and sometimes our ways of relating to others aren't the best for us. I am also a cancer survivor, and I understand that having serious health issues and dealing with bad employers and family issues like elderly parents and uncooperative siblings can certainly leave us drained and anxious. But you can get through this and things will work out.
For your own self esteem and reassurance, you may want to quietly begin exploring possible other jobs in the area that you might get part time like this. I've heard "I'll never find another job...." a few times in this post, and while it's true that as we get older (what age are you, by the way?) and have had health issues we are less and less of an employment prize in the eyes of some employers, there are potential places we might fit in other than the place we are now in.
When people are in a work situation, they tend to get focused in on this situation, but in reality there are other things and a whole other world out there. Best wishes to you moving forward.