When does a woman experience a wet dream, and does this occur from the onset of her puberty? What is the ruling of Islamic law regarding her not knowing about a woman's wet dream until after marriage, while remembering sexually arousing dreams before marriage?

There is no specific age for wet dreams; it is one of the signs of puberty. If a sleeper dreams that they are engaging in intercourse, wakes up, and finds seminal fluid, then ghusl (definition) (ritual bathing) is obligatory upon them. Otherwise, nothing is required. If you see seminal fluid and do not perform ghusl, then your prayer is invalid and you must repeat it. However, if you do not see seminal fluid after exciting dreams, then nothing is required of you.