Read the whole thing. No skimming. That is a hard situation.

To start, you are neither worthless, nor unloveable.

So is your sister nearby to there? She does need to be apprised of the situation.

If it's any consolation, I don't think it's terrible thinking on your part wondering how far they should go extending her life. It's her call of course, but for thinking that, it's not bad. (It's why I personally have an advance directive. I know what I want/don't want and don't want to put anyone in a position to wonder.) Does she by chance have one? It's a practical matter, though many avoid dealing with such things.

I have to wonder what help might be available. I certainly don't think it is on you. A call to the local agency on aging might provide some useful information.

Are they in a city or town where you could have your throat looked at? Like a place you could get to without involving them?

I'm so sorry that you have been invalidated and abused. You didn't deserve it then and you don't deserve it now. Sending protective thoughts your way. I hope the flashbacks ease.

ETA, I agree with WC. You need to be your first priority.