I sympathize with that and I don't think it's wrong to buy things that are offered for sale in good faith, unless she's also doing something like arriving early and combing the stores for them regularly. But at the same time, the overall amount of clothing going to landfills doesn't do anything to ameliorate the issue. There's a huge shortage of plus sized clothes in thrift stores, and after having worked at a thrift store in Finland I can say the shortage is probably global. They were asked after constantly and tended to even be priced higher, or let through with lower standards, due to the demand. Buying clothes, particularly femme ones, for plus size people new in the fast fashion society we now live in is actually sometimes impossible, in the sense that it becomes too much to afford or too far to travel to fill whatever functional need a plus size person might have. So yeah, I, personally, would want to make sure that if I bought one in a thrift store, it was one that had been sitting there unsold for a month and the people who might come looking for it had definitely had a chance to find it.