Don't waste rubies to combine 2 S units, just feed em B and C units with friend points and random drops. Might take a while but you should save your rubies to enhance SS and SSS. Personally I'd combine for another SS with a bit of patience and then probably sacrifice Veri, most SSS dps you'd get would be better than her. It's a bit of a gamble though, you might end with one of the lowest tiers, or a bad single target healer SSS like Konfi. As they say, there is no gain without risk.
Ps. Fuck those little bastards chain casting Unexpected Lightning, there is a spot reserved in hell for you.