I understand that aparece means 'to appear' but for an English translation it should use the English equivalent. We would never say "she appears in the morning." We would say "she arrives", "she will come", "she gets here in", "she will be here" etc. Maybe I am wrong but I feel it would be better if it were a phrase we actually use in English.
My formal study of Spanish was many years ago, but the lesson on "aparecer" I remember, as the instructor was very dramatic on the point. It does mean "appear" but the meaning has a sensation of suddenness about it, rather than the sense of "arrival" that you give in your example. I.e. in the way a ghost (an apparition- there's your mnemonic for this) might "appear" in a room suddenly. So this sentence of "Ella aparece en la mañana - She appears in the morning" has the flavor of "She wasn't there, and then she was", hence the other comments in this thread saying things like "Is she an illusion?"(Willy84k) and "I wonder where she's been?"(AnaKK99) and about the neighborhood cat who appears in the morning (HolyT). So "She appears in the morning" is a correct sentence in English if you think about it in those kinds of contexts. The English usages of appear as you are thinking of it in the examples you give are better expressed in Spanish with words like "llegar - to arrive", "presentarse- to present oneself", "venir- to come".
A side note about the word "aparecer" to be careful of, is that it does NOT mean appear in the sense of "resemble" or "seems". For example, the English sentences "she appears tired", "she appears to be digging", or "In her looks, she appears a lot like her mother" would not use "aparecer", but rather the similar words "parecer"and "parecerse a" ,but that's an entirely different grammar lesson.
This is a very common pattern for verbs ending in -cer. A c before an o is pronounced with a k sound, so it must change to maintain the soft c sound in the stem. Perhaps for Spanish speakers, -zco may be a bit easier to pronounce than -eso, or perhaps it makes for a more definitive verb inflection.
"Mañana" can mean both "tomorrow" and "morning", but, as I understand it, "tomorrow" is used as an adverb, while "morning" is used as a noun. Since there is a "la" just before it, you know it is a noun here. If this sentence were saying "She appears tomorrow," it would be "Ella aparece mañana."