Yeah, Eclis and Penny's relationship is fucked up. They're both using eachother this that, but let's not forget that Penny just sees them all as characters in a game- because that's basically what they are.
Girl has her priorities straight since day 1: which was to LEAVE that game as soon as possible, I can't blame her for what she does because all she wanted was to survive. She's been planning on leaving since she transmigrated so ofcourse she won't give a damn about using Eclis for her own good.
Ofcourse this doesn't justify shit tho... but I can understand Penny's side much more than Eclis' (I've also read the novel so maybe thats also why..) though let's not forget the real weirdo here is "Mr i'm in love w my adopted sister"