Much as I'd love to believe you- we can't assume the flustered bit is an act. Unless you actually know Sinder or have information about her you're not sharing, we have to go by her actions- which are that she doesn't like to show anything. Also, the last time she saw her audio or live RP clip or whatever on R34, she stopped doing them for a while. Coincidence? Maybe.
As for the cosplay pics- yes, you're valid for saying they're too expensive for what they don't show. But, again, Sinder has a habit of shying away when things leak. And she does find out. It wouldn't surprise me if RED trolled these forums looking for her former friends and whenever he sees Sinder's stuff he gets mad that they're losing money.