There's always a question with the Princes of Oblivion, whether they can be counted as "good" or not. With the likes of Molag Bal, Mehrunes Dagon, and the like, the answer is clear on the side of "bad daedra". Sheggy and Malacath, though officially labeled "bad daedra" in Morrowind, are often recognized by us as more "alien", "outside good and evil" or what have you.
Then there's Meridia: shining light against the undead. A clear example of "good daedra", is she not? Bringing the light of holy vengeance against abominations of darkness, you might think of her followers as natural allies of the followers of Arkay, in particular (and also Stendarr, as seen in Skyrim).
But the thing I only just realized about Meridia is that she's not good, not really. Sure, her actions are usually beneficial to the living... but do we not regularly have debates over whether, for example, Vampires can be considered "always evil"? For example: consider Janus Hasildor, who has long and ably ruled Skingrad. While others might consider him eligible for an exception, not Meridia. For Meridia, he isn't the exception to the rule; he's the PURPOSE of the rule.
For the Daedra are always, in the final anolysis, more aligned to Padhomay than Anu, and Meridia is no different. Vampires like Count Hasildor are very much like those selfish few among the original spirits who were not content to appear, live for a time, and then return to the flux of the void, but rather continued their present existence at the expense of the future, ruling over and absorbing others of the original spirits.
So whether you have a society that is terrorized by undead, or a well ordered society ruled by a cabal of mostly benevolent vampires (who actually do a better than average job ordering society and upholding justice, and who do an excellent job regulating vampirism in their area), Meridia doesn't care. She's there to destroy abominations, not engage in philosophical discussion.