I think you may like Minnie better than Ella but are not sold on Minerva.
Maybe use Ella as a middle. I like Melinda nn Minnie
Some names to get to Minnie
It's a bit old ladyish (but in keeping with Minerva) what about Muriel?
Sadly DH has a relative named Muriel who he doesn't like and so has vetoed it. We have no problem with old-ladyish names in general :)
Minerva! It's beautiful and underused. Minerva and Arthur also make a great sibset!