I think some of the anger/rage you are feeling is because of feeling "stuck" and like there is no way to resolve this issue. You don't like being frightened awake and yet you are afraid to try and work with your sister on a resolution or even express your resentment at being awakened.

happiedasiy has pointed out that ear plugs and sleep aids are probably not a good long-term solution. I would wake enough next sniff to do a "startle" reaction, "Oh! Your sniffing like that scared me! Are you all right?" and at least get it out without accusations or demands that she change. See if anything happens over time if you do that a few mornings in a row. Just making it known that it has disturbed you might keep your anger from building up and will notify your sister in a way that she cannot dispute/deny ("I am scared" is not something others can say, "No you aren't" to very easily/believably :-) and the extra "Are you all right?" defuse any anger on her part -- you can say you did not know if she was crying or had gotten a cold, had allergy/sinus problems, etc. and acting concerned about her instead of angry at the sound might help her become more aware of it.

Or, have you thought of going to bed and getting up earlier than your sister? :-) I would maybe set an alarm to go off, something that won't scare me when I wake or that I control. If you want to be angry at your sister, you can then explain that you prefer waking under your own power instead of being scared awake by her. But I think you should try a kinder way to at least make sure she is aware of the loudness/issue. You and your other sister have talked about it but no one has told her. Remember, how we sound to ourselves and how our habits affect us and our awareness of them are totally different from how they may affect those around us?