Your ideas are pretty good but I feel like there is one possible huge issue with it by your theory. Asuka joins the student council as a secretary after Yamazaki is already president. If memory serves me correctly we know based off of when Miyamura became president, this happens at the start of a new school year where the student council president must pick his council members. If what you're saying is Asuka doesn't approach Yamzaki until after he becomes president, that would mean the secretary position was open for the whole period of the beginning of the school year (which when I googled when the Japanese school year starts, it said April) up to the point Asuka notices Yamazaki (which she states in this chapter is November). I find this difficult to believe when it sounds like the secretary position is important as it is the president's right hand man so you want someone either trustworthy (Yamada to Miyamura), or someone especially talented (Shiraishi to Tamaki if he became president in the avoided future).

My point is first, its incredibly strange that we have no idea who held Yamazaki's secretary position before it was supposed to be held by Asuka. I can see Asuka becoming secretary due to being exceptionally talented, but she never met Yamazaki until halfway into the second term of her school year I have a hard time believing she just magically joined the council as secretary soon after discovering who Yamazaki was. Something was made as as a reason for Asuka to approach Yamazaki so Yamazaki could see the amount of potential Asuka had to be his secretary. I believe that to be her request to rid herself of her witch power which gives us a time stamp of when it happened sometime after November. This is all theoretical of course, but the main point is that it wasn't her feelings for Yamazaki that made her hate her witch power when by my theory it was before she joined the student council and got to really know Yamazaki and fall for him that she got rid of her powers.

I must confess though, I'm not much of a guy to try and theorize so much so I might sound completely off. To reiterate my point from my original comment, I feel like the fact we as an audience need to speculate so much on the events surrounding Asuka to make her backstory make sense seems like pretty poor storytelling by the author still.