Hi throwawayaccount

I'd say that it could be hard to say what a "normal" person might do, and if she's trained in gymnastics there's a good chance the "average person" may not have been able to push her off.........
But the "average" person (without depression, as you said you think you suffer from), well, I'd hope they wouldn't feel ashamed............
And the depression could be a big part of this

The way I see it possibly is:
Getting her off you and what you said...........well some of the feelings that may come along with depression can be weariness, feelings of futility or hopelessness or powerlessness or lack of self-confidence or feeling "I'm nothing more than....."........and if they're not already in the forefront of how you're feeling, someone treating you like that can easily push them more into the forefront...........
So please don't "beat yourself up" over this
And before you see it as a weakness (!!), some of the strongest people can suffer with depression and equally some people suffering from depression are the strongest people.
And you can still have self respect........she was wrong not you.........you did all you possibly felt you could do under the circumstances..........and depression has that much to "blame" for........which is not your fault

And setting boundaries............well maybe rule out the playfighting?? But on a day-to-day basis sometimes that can be easier if you can try to learn and/or recognise signs where she might be edging on "unacceptable" behaviour/s and stepping in quickly with "No......." or walking away before her behaviours escalate...........
But yes, it would definatly be a good idea to tell your parents...........and you don't even have to tell them everything...........but both for your sake and for hers

And sorry I missed commenting on this in your first thread but:
"This is like the most pathetic thing I've ever typed out"
I honestly don't see it as pathetic in the slightest
My heart goes out to you in finding yourself in a situation like that..........to summarise, you're telling us that you feel you have depression, you have a sister who maybe has real problems, has behaved in a totally "unaccepable" manner and subjected you to an extremely upsetting experience..........that is not pathetic
In fact I'd say that you should feel proud of yourself in voicing all of that!!!
Now I don't know if we can help with your sister's problems..........we can certainly try..........but I'm sure we can offer you some support with the way you're feeling
Good on you for speaking out!!! Respect!!!

Alison