I think that what them mean is that they are, in every way, Druids of 7th level. Except for that they aren't druids. Although it shouldn't say "replicate". I would assume that this is an oversight. It should say that the nymph prepares and casts spells as a 7th level druid.
Monte Cook wrote an adventure where there was a nymph NPC. She had her spells picked for her already, in this format: 2nd-barkskin, flaming blade (x2), 3rd-poison, etc. Just like a druid. Solars and some other celestials cast spells like this too.
Their spell-like abilities are all ennumerated as to which spell they replicate, and how many times per day they can perform each.
Then it says they can cast spells as an Xth level cleric.
This is all clear and unambiguous.
Monte Cook wrote an adventure where there was a nymph NPC. She had her spells picked for her already, in this format: 2nd-barkskin, flaming blade (x2), 3rd-poison, etc. Just like a druid.