Susan thinking of talking to Grace about personal things was a relatively late idea, but I loved it on all the levels.
I, of course, laughed maniacally upon thinking of it.
Actually, that's not true. Not the laughing maniacally bit, I totally did that. There are aspects of this that aren't late ideas. Specifically what was a late idea was this level of escalation from "maybe there are things Susan will talk to Grace about at some point" to "Susan is contemplating using Grace as a sort of therapist".
Which possibly doesn't sound like the most rational of plans, but panels three and four, so there.