Summoned +Atk -Spd Ophelia, what do I do?

Focus on the boon, I've got the same and went with Blazing Light, Death Blow, Chill Res and support C slot or Res Smoke. If she has 2 external sources of cooldown (pulse skills or mage allies) she starts with a Blazing Light which, from her massive attack will devastate a lot. If you have Special Spiral (I just got one in Hero Fest but haven't given her it yet), it means she gets Blazing Light ready after her first combat so she'll basically always have it. She's deadly on player phase and doesn't really need to double but she is weak on enemy phase due to her low speed so the Darting Stance seal can help.

Should add, watch out for DC+Vantage. Blazing Light will put anything into Vantage range so they'll hit her first before she can remove what little HP they have left.

Atk is easily her best boon, a bane in spd can hurt but you can still easily work with that, you either use her base kit or go with the ipernuke build an AoE special, Life & Death in A and Special spiral, basically you will have the special active all the time and nuke whoever comes close to her