In this first appearance of Mayday's Diary, it's used to recap readers on the events of the past year's-worth of published Spider-Girl stories, presented in May's own words.
Mayday's Diary is again used as a framing device when the series was relaunched with Amazing Spider-Girl #0, providing a more plot-relevant recap of the events of the previous Spider-Girl series.
Finally making the leap to a physical in-story appearance, Mayday's Diary shows up in Amazing Spider-Girl #25 when 'April Parker' uses it to catch herself up on recent events in 'her' life.
Probably apropos of nothing, but the diary looks different here, though there is still a flowery-theme.
Perhaps May's old dairy simply ran out of blank pages and this is a new one she started in Amazing Spider-Girl #0?
I realize this is nothing earth-shattering or exciting, but it helps ground a fictional character like Mayday in the real-world when she uses such a mundane, everyday item like a diary. A nice touch. I may be mistaken but I believe these are the only instances we see Mayday's Diary. Please do let me know if I'm wrong.
Until I get replaced by my symbiote-clone hybrid, I remain
frogoat