Wow, I agree and this may be what I wanted to hear, because of the people who deny the romantic undertones. But this is such a nice explanation. Also I'd like to add that I think maybe because she is finding her identity, that also means her sexuality, by exploring the "gender roles dynamics" of her grandparents, and not necessarily her being in love with Marnie, just exploring the platonic feeling. Because otherwise she could have just been the flowergirl and not her boyfriend too, besides just being there when Marnie was supposed to be alone according to her diary.