This is step one: Develop a thick skin. Barring that, self-publish on a blog you control, or in a publication you control. There really is no in-between.

Any time you submit to any publication, you must (a) follow their submissions guidelines; and (b) accept their edits (unless they explicitly state, "I want this, but it would be nice if you would change this - are you open to that?" Many, once the piece is accepted, would simply make such changes themselves - and would be within their rights to do so (generally, assuming that's in their submissions guidelines).

I have had writers mangle pieces because they did not understand the edits I suggested, and that is heartbreaking. Exactly the sort of thing your sister pointed out. But to avoid that, you have to learn to take the feedback that makes good sense to you, to ask questions if it doesn't, and to reject it, yourself, if it's crap. That takes practice. I'm not sure it can be taught, this sort of discernment.

You cannot let anyone crush your spirit, period. Protecting your spirit and your love of writing is your job. No editor is trying to tear you down. In fact, the hard truth is that they're not thinking about you all that much, or they are holding back something more critical because they WANT to be nice and protect you from being hurt by them. Whatever negative things they say about your story are not about YOU or your worth as a human being - you have to remember that. You have to remember that they are looking at a whole bunch of produce (stories) in the market, and they only need to fill a small basket. Someone else may want the peaches they leave behind. Or not.

Stephen King's novel, Carrie - the one that launched his career - was rejected something like 15 times before it was published.