I don't think so. If the phrase in love with Jane Eyre were a prepositional adverb phrase, it would answer one of these questions:
3. "In what manner?"
4. "To what extent?"
Clearly, it does no such thing. It would have to answer the question Where did he fall? Well, he didn't "fall" anywhere! The reason it doesn't answer that question is because "to fall in love" is a phrasal verb in which the word "in" has lost its normal prepositional function. That's why prepositions that appear in phrasal verbs are often referred to as particles. They're not really acting like prepositions anymore.
Hope this helps at least a little.