I'm still sticking to Moghedien as the possible teacher for Delana, while agreeing with you that Granedal would be a more logical choice. But barring her, I think Moghedien is the only logical option.

And I don't think Nynaeve meant "subtle" to mean complex with respect to Delana's compulsion. I think Kerb's personality itself had been erased by the complexity of Graendal's compulsion. Delana's compulsion on Ramshalan obviously had no such effects. It was subtler in the sense that it was simpler.

As for Aran'gar not compelling Egwene... I think the reason is obvious. Egwene tells us she learned compulsion from Moggy and how to counteract it. This is almost certainly info Moggy gave Moridin who probably gave it to Aran'gar. No point trying something that would definitely raise Egwene's suspicions while also proving to be completely useless.