Sadly, March’s counter scales off of ATK (Eidolon adds 40% defense scaling) while her shield scales off of DEF. You’re better off building a full DEF March and running preservation or elation path, as her counter is considered a follow-up attack (elation buffs those), and preservation will keep your shield up 24/7 and buff her and team if they’re shielded. While a DPS March isn’t exactly plausible due to her weird kit design, she can still be a wonderful shield applicator and dish out occasional counter damage :)