You want Selene on Obey because she'll blow Fey Wind as soon as it is up. She doesn't care if the boss just jumped and became invulnerable because of a mechanics phase, which is a horrible waste.

Also, sometimes she'll blow Fey Caress when someone gets hit by an undispellable status effect, and then it will be on cooldown when you actually need it for something critical. This is hardly ever the case in raids and trials, but I have found she's pretty handy in 24-man raids. There's hardly ever too much healing requirements in 24-mans save for perhaps Scathach and Diabolos+Diabolos Hollow, so WD is less useful there. She's also really good with Deathgaze's Dooms and bleeds, Forgalls' poisons, Ozma's bleeds and Calofisteri's wounds -the last one in case the main tank fucks it up and cleaves the entire alliance with Haircut after Depth Charge.

Her Silence doesn't see much use ever, but if you ever need it you need Obey for it too.