In your circumstances, would it be possible to quietly disengage, twinklestar2?
Will your sister notice / care if you sidle away and can't be pinned down?
If she won't, then the easiest is to answer texts a few days later, then a few days later still. Same with emails. If you see her in the same room, simply try to find others to talk to. If she corners you, never give her personal information and treat her as if she was a work colleague you only tolerate; polite, no particular warmth. If she starts being abusive, leave or make sure that you move to a place with witnesses; people often behave better when others are around. Don't contact her.
Never get drawn into an argument. If she tries to start one, treat her as if she was a difficult client/customer.
If mutual family members talk about her, stay silent or with neutral mmhmm noises. If they accuse you of withdrawing from her, say that you aren't, you just aren't particularly close. (this sort of situation is very hard on mothers, but they can't enforce closeness between siblings even though it is saddening).
If she will notice and cause a fuss, then it's harder and there's probably no way to avoid some waves. But as long as you say polite, disengaged and clear then the storm passes ... Eventually. Its harder when kids are involved though.