Meridia Lore Question

Faustes

Is there a reason why Meridia doesn't care if your character is an undead vampire?

Anvos

Well the pc is a member of Lamae Bal's clan who are in this era staunch anti molag bal.

Plus its debatable that vampires are the same as necrotic undead, since vampires retain their overall free will which means their not a renvant even if their sire has some limited influence over them.

Also you never truly die to become a vampire.

WhiteCoatSyndrome

Probably because the devs didn't care enough to put in a dialog option for that, but less pessimistically: she can put up with one vampire PC, or her hated enemy Molag Bal winning. So she chooses to look the other way as long as you serve her goals.

Shaarizad

True. Just like many of the other Daedric Princes, Meridia is a manipulative schemer willing to do quite a lot in order to get what she wants. Even if you were a full-on child-of-molag-bal vampire, if she thought she could use you to get what she wanted, she'd do it.