Need help with an Eirika build

Seems solid enough, there's not much room for Eirika to shine outside of buffing her teammates though.

Few thoughts here, I'd inherit Rally Defense too, so you can switch the DEF/RES increase if you need that extra boost. You can also free up a seal slot by using a split rally skill, however you wouldn't be able to buff as many allies to the maximum.

A good A-slot to consider would be Distant Defence 3, as Eirika is generally sitting behind teammates, so she is less likely to be hit by melee attackers, this would also turn her into an excellent mage-bait as her high spd/res prevent her from taking too much damage from fast mages. Fury isn't a bad choice either.

For B-slot you could try running shield pulse along with your Aegis/Pavise but swordbreaker 3 is generally the best option as it helps mitigate damage from melee attackers. If your Eirika is -Res, you could run R Tomebreaker for magic mitigation. Renewal isn't a bad choice either.

You could probably try experimenting with miracle too.

Keep in mind, the tests you're running (I assume you're using kagerochart) don't factor in skill inheritance so I suggest to try pitting some of Eirika's common checks against her and then adjust accordingly.

Hope I helped.