I actually think the worship of Meridia could be more complex, both philosophically, and from a game play perspective. If you read The Invocation of Azura, you can get a better idea of the kind of worship expected by the Daedra.
Invocation of Azura (Morrowind) said:
Azura is the only Daedra Princess I have ever worshipped who seems to care about her followers. Molag Bal wanted my mind, Boethiah wanted my arms, and Nocturnal perhaps my curiosity. Azura wants all of that, and our love above all. Not our abject slavering, but our honest and genuine caring in all its forms. It is important to her that our emotions be engaged in her worship. And our love must also be directed inward. If we love her and hate ourselves, she feels our pain. I will, for all time, have no other mistress.
While the book shines a light on how divergent worship can be from one Daedric Prince to the next, it also highlights how a simple concept -- for instance: Love -- can have far-reaching influences on what constitutes worship. Abject slavering is discouraged, because mindless dedication is not love in any form, however, if you cannot genuinely offer up your love, you cannot truly worship Azura. What this demands, then, is not just the ability to honestly say you love Azura, but the necessity to offer your pure devotion. As a mother loves her child without reserve and without question, Azura demands you love her as well. It seems simple in concept, and easier than dedication to Molag Bal for some, I think there's more to be taken into consideration before making a decision.
The worship of a Daedric Prince can be simplified to the concept of identifying their most prominent feature (love; deception; secrecy; betrayal) and embodying the totality of that concept's possible permutations. Boethiah pleasured in her worshipers being warriors, but in such a way that carrying out violence against each other, killing each other in celebration of her name brought her the greatest pleasure of all. Molag Bal relishes "blackmail, extortion, and bribery", requiring a worshiper only be the sort of person to cast aside the cumbersome trappings of social morality without hesitation. Azura, on the other hand, requires love. Requires it. It's not a matter of being conditioned by society to feel no guilt in returning the short end of the stick you were dealt, or giving in to baser, more violent urges society (probably very wisely) discourages. To give your love requires conquering fear and hesitation, opening yourself up as you never have, and pouring that love out at her feet without reserve. You must love not only a Prince, but the concept of a Prince, whether that Prince manifests for you or not.
Because of this, while I think the worship of Meridia, about whom we know little thus far, can indeed be boiled down to "kill all undead", it should also include as many permutations of the concept as can be fathomed. "Cleansing" is her energy. Sunlight, heat, fire, holy burning. Don't just avoid necromancy; eradicate all necromancers; seek out vampire dens and obliterate the inhabitants. In this, Dawnguard is a blessing, because you can complete the quests as an agent of Meridia, cleansing the land of undead in her name.
She also strikes me as being firm and unbending in her will. There is no grey area when you cast so much light; you can only see the black and white, since you blind yourself to what grey there may be. You either worship her, or you do not. Whatever she may appreciate of those who happen to kill undead, I doubt she would see it as "worship" unless that is the cause and drive of the character. I see there being something of a Paladin mentality, though perhaps not so severe an attitude as the Vigilants of Stendarr.
I only focus on Meridia here as that's the Daedra I have set up for my own character to follow and worship, so I've been giving the subject a little extra thought as of very recent, but I do think the Daedra expect far more activity from their worshipers than the Aedra, and I've yet to see a Daedra unwilling to sacrifice dissatisfactory worshipers on the potential for something better. It's not enough to disown a Champion; they want to see them dead and punished for failing to represent them. Obviously there's greater expectation to satisfy a Daedra when you're their Champion, but it's only because you were the best gods damned worshiper of the bunch! You know, until the Dragonborn swans in and loots your corpse for artifacts with no intention of honoring a holiday in any name but their own. But unless an unaffiliated player character unhindered by restricting mechanics interferes, the implication is that embodiment of ideals specific to that Daedra is what grants Championhood, and the logical conclusion about those who can call themselves "worshipers" is at least some level of dedication to embodying those same ideals, if only to a lesser, or less socially observable degree.