Through covid I have followed the rules as best I can, stayed at home unless going to work/food shopping, isolated if I'd come into contact with someone who tested positive etc... I've always had a funny relationship with my sister and we seem to clash quite often. I've always felt that she thinks she's better than everyone else, entitled to do whatever she wants - 1 rule for her and 1 for everyone else...
Anyway, a couple of months ago she went to a party with a few friends and the party was hosted by an old friend of hers. They were there for a couple of hours I think, had food and drinks then went out to the pub down the road. Next morning old friend messaged everyone to say that she had tested positive for covid and would be forwarding everyone's details to track and trace. Everyone asked her not to, as some people couldn't afford to take the time off work to isolate (I'm not saying it's right btw but I do understand). The friend did as everyone asked. A day or so later my sister messaged me to say that she was on the beach with two of her friends who had also been to the party (when it was really busy as all the holiday makers were visiting at the time) and asked if I wanted to join them. I had plans so didn't go. At the time I did think it was quite selfish of them as unlike work reasons, a beach visit wasn't necessary but I kept my thoughts to myself. I'm not the covid police after all and it would only cause arguments if I voiced my opinion.
Fast forward to last Friday when I visited my friend. I didn't tell her I was going as I was just passing through and decided to knock on and see if she was home. She explained that she hadn't been feeling very well the last few days and it was probably best that I didn't come in, although she was confident that it was just a stomach bug. I was desperate for the loo (thank you McDonald's tea) so asked if I could just pop in quickly to use the loo. We didn't touch, hug, anything and I left after using the toilet. I was in there 5 mins max. Told her I would pop in when she was feeling better. Anyway, friend messaged me on Saturday morning to say she had tested positive. I've decided not to take a test or isolate (unless I start to feel ill of course) as I think it would be quite extreme given that I was only in there for 5 minutes and we didn't actually come into close contact.
I told my sister earlier about my friend being unwell. She decided to give me a huge lecture about how I should be taking a test and isolating for the next 10 days. It is really irresponsible for me not to do so 
I honestly think she's forgotten about what she did two months ago. As the peace maker I try to hold my tongue as much as I can, more so because I just cba with the argument or hassle. I think she thrives on the drama between us sometimes. But please tell me I'm not wrong here and the two situations above are completely different??