Giving Est her old lance back

Use Valter for that, fam. Or Hinoka. Or at least someone you can put safely in front of an armored unit that doesn't use magic.

you could get a separate est to 5 star and inherit the heavy spear+ on your 4*+2, so that way you can get a 4*+10 with the heavy spear+
(Reminder do not refine the heavy spear until you inherit it, if you plan on doing this)
although you would be better off making someone else an armor killer, she only has 24 def, but if you want to use est for the job, go for it

They did a poor job on est, if you played SD you would know est have one of the best growth rates in the game but here shes just.....disappointing.