Well lets see what we know. Spoiler Caster said she used a command seal on Saber in the recent episode and Saber is resisting because she can resist 1 command seal. Caster also said that "Your servant body cannot resits me". While Saber has her ass stuck up in the air. From that I can assume Caster used a command seal to make Saber be a horny slave or something. As for the wedding dress, maybe Caster has a wedding dress fetish. I suppose using more command seals would end Sabers suffering and enable Caster to get what she wants, but Caster is a sadist, so whatever. I liked the episode btw, I'm looking forward to the battle scenes because that's when the anime looks weally weally pwetty.