Is your sister a different clothes size to you? I think due to the reliance on AI, Vinted has some very blunt detection tools.
Since losing weight I've sold a lot of my old clothes but I also have some old clothes from before I put on the weight. I'm wary of putting them on straight away because I've read instances of Vinted interpreting have a wide range of clothes sizes as buy-to-sell. I know people do buy to sell on but it's really not unusual for women age 30+ to have bags of clothes across the size spectrum.
I've also got a pile of young adult male clothing - Superdry type stuff I'd like to sell but again I'm wary of looking like a reseller when in reality it's just clothes the DS's no longer want. They'd be happy bunging them in a charity bag but I paid for most of them and I could buy some beauty shite with that money!
Vinted is great for the speed you can shift stuff but also really awful when the slightest thing goes wrong and has unreasonable, nonsensical rules. I feel lucky not to have been banned yet, just had the odd item removed. Every time I upload though I'm half expecting it.