Panel 1: She goes on to say that after each day's unproductive stalking, she would go home, turn into an Indigo Tribe energy construct, sit in Jim's recliner and smile stupidly as she recalled every sentence and every glance.
Panel 2: She drew pictures of him, she composed songs about him and she wrote down her deepest personal thoughts about him. This caused white Valentine hearts to appear in mid-air. Ah, well. At least she never stood around in a hallway shouting HORMONE ATTACK!!! as he passed by......
Panel 3: Since she lives in fear of her mother's reaction to everything, she tells Connie that it's a good thing that Marian never read her diary as it was so full of teenaged lust and desire that after a while, it smoked. Personally, if I came across someone who looked like Teenage Elly does in this image, I'd be more worried that she'd crapped her pants than I would about her having TV-Y7 fantasies about some donkus with a paper route.
This is because Elly still thinks that if her mother ever saw it, she would be publicly disowned and sent to a home for wayward girls. The joke is on her because if Marian ever read it, she'd probably be ashamed of herself for not noticing that her little girl was a twelve-cylinder wackmobile.
Panel 4: When Connie asks her if she hid it, Elly says that she burned it.
Summary: First off, I think that Elly's idea of what constitutes scandalous behaviour has always been rather off-kilter owing to an inability to admit that her mother isn't trying to destroy her and also being the dullest human being on the planet. Second, if her writing style is anything like Mike's, Marian's reaction to what she might read would probably be confusion owing to the windy, elliptical and poorly constructed tangle of verbiage she'd be forced to wade through. She wouldn't know if Elly liked this boy or if she wanted to kill and skin him.