Are you relying on her for a lift Alie2Oxon?
Otherwise this doesn't really make sense.
She tells you to go to Asda instead of the nearest cash-point, you say, "no dear, I've planned my day, starting at the cash-point... talk to you later, bye-ee"
As for the wider problem of friends offering 'helpful' advice - I understand, I'm 84 and bereaved last year. Well-meaning - and they usually are - friends and acquaintances frequently give me the "why don't you join xyz, you might enjoy the activities" or "I think you should zyx..."
It's frustrating, I know.
My close friends and family are aware that if I genuinely need help or advice, I will ask them and equally genuinely listen to their advice or take up the offer of help. Because they know that, like them, I have a mind of my own.
It ruins your day, I know, when you have it planned and something or someone comes along and derails it. Talk to your sister, quietly without anger, and tell her that your autonomy over your choices is important to you.