@Hela,
Hela, please be advised that I am no teacher, and am far from being an expert on proper grammar. Anything I say is just based on my experience (in hearing/reading) and my personal thoughts/conclusions.
Let me first say that your proposing A vs B as alternatives is somewhat confusing, because I see both as incorporating a number of alternatives.
My thoughts are along these lines:
1. For the sake of consistency and symmetry, many would probably prefer to stick with one tense throughout.
2. I don't see any problem with changing tenses in new sentences/clauses if you have already established the (past) context. People will understand what you are trying to convey without a problem. For example:
"as soon as even the smallest drop of rain (5) fell / had fallen, she (6) scuttled back into her house and (7) locked herself in her bedroom!" seems fine to me, even if you select "had fallen." The "as soon as" preface tells you that, although literally stated in the present tense, it is the past tense that is intended, and which applies, even when you proceed to mention the "scuttling" and the "locking."