The object of a preposition comes after the preposition that heads the prepositional phrase. The prepositional phrase, including its object does not "always come after a verb." So I am not sure what you mean by that. An example is In the summer, we all go crazy. Yes, 'school' is the object of the preposition 'in' in the prepositional phrase 'in the school'. Yes, the subject of the independent clause is 'daughter', and 'student' is the subject complement. The independent clause is 'Her daughter was the only student in the school.' 'who won a prize' is a relative clause that tells us something about 'student', and also about 'daughter', since 'student' refers to daughter. Relative clauses often immediately follow the noun that they modify, but they do not have to, as in this sentence. We have the prepositional phrase 'in the school' that comes in between the relative clause ('who won a prize') and the noun it modifies ('student'). 'prize' is the direct object of the verb 'won'.