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Quick Riposte is a must, Distant Counter makes sense with Quick Riposte's enemy phase nature, her very decent Res, and her adaptive damage. Iote's Shield (as a seal) is optional if you want to remove the weakness to arrows and odd tomes. (If you do give her Iote's Shield seal, she's a reliable counter in one unit to non-Firesweep Lyn and Reinhardts, and that with flier positioning: very handy for arena.)

If you give QR as a seal, there's a lot of handy B skills you could use, like Renewal or Guard. You could also run Axebreaker to leverage against non-B! Hectors on both offense and defense.

You can run Aether without acceleration for maximum points - it would make her recursive as well (restore her HP without a healer, potentially reentering QR's threshold even after falling below it, etc.). Ideally, she could trigger Aether after 1) receiving 1 attack and dishing back 2 on enemy phase, 2) attacking once and netting a kill on player phase, 3) receiving 1 attack and dishing back Aether on enemy phase again. Otherwise, she could trigger Aether in one enemy phase if QR holds up for 2 combats, but it likely wouldn't restore much as Myrrh's first hits tend to hit hard.

Sol might actually be a good choice, for the reason given in that last sentence. Assuming no slowing, it'd always trigger on the second enemy phase combat.

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