[Facts] Re: Seeking Name Meaning Unexpected/Surprise
This is hard!
I found 'Nenad', a Croatian and Serbian masculine name meaning "unexpected". I suppose you could make it feminine with Nenada?
Apparently the Latin name Proserpina means 'to emerge'.
Epiphany -- from the English word meaning 'sudden appearance' or 'sudden perception'. It would usually be given in honour of the Christian feast day by this name commemorating the visit of the Magi to the Baby Jesus, but it could obviously be used simply for the English word, the same way the names Felicity and Hope are used, for instance. Other forms of this name, its Greek origin meaning 'manifestation' (as in sudden manifestation), include Epiphania and Epifania (Spanish).
Aristophanes, a Greek masculine name which means "best appearing", could potentially be made feminine with Aristophania.
Aparecida, Portuguese feminine meaning "appeared". It comes from, and is given in honour of, a title for the Blessed Virgin Mary. However, it could be used simply for its actual word meaning of 'appeared'. (in this sense, 'suddenly appeared', which is where the Marian title comes from, the statue suddenly appeared out of nowhere)
I guess the English word Serendipity could be used, but it's not quite what you mean, though it is related. (I think it's a little weird, though)
The English word 'admiration' comes from a Latin root ultimately meaning 'to wonder at' and could also be used to mean 'surprise'. So Admiratia might work.
Names that mean 'miraculous' or 'miracle' could also fit with your meaning... Milagros is the usual Spanish form, meaning plural 'miracles'. Milagra is a feminised form of 'milagro' (miracle) that I think sounds nicer.
Karishma is 'miracle' in Sanskrit.
Nessa means miracle in Hebrew, and Alazne means miracle in Basque.
Vismaya is Sanskrit and means surprise or wonder.
Prakhya is also Indian (not sure if Sanskrit or Hindi), derived from a word meaning 'appearance'.
My only other suggestion would be to look up words such as appear(ing)/appearance, emerge/emerging, surprise/surprising, unexpected, miracle/miraculous in other languages and see if you could adapt or use those words to make a feminine name.
Hope this helps! :)