5 star Anna is a more versatile Minerva without the flying dragon weakness. Anna can also do more damage because of her skills.
Their stat growths and averages are pretty similar.
If that's an option, I would recommend that.
If not, you should just keep it only because her job is to go kill of blue characters. She has too many weaknesses for the additional defense or resistance to do too much of an impact.
I read somewhere that wyverns don't get the dragon weakness?