So a few things occurred to me while I was checking the different routes to make sure I wasn't just picking the worst choices for Dylan:
The only difference in Ellie's reaction during the Sophia/Ellie scene on day 18 between the boarding school route and the self-defence route is on the boarding school route Ellie is excited about Dylan being away so she can sunbathe naked. If he doesn't go away, it's just business as usual, regardless of the route. Ellie can mention Dylan being the reason she doesn't sunbathe naked on day 3. Makes no sense she'd bring it up now just chatting with Sophia
You don't even need to be on the Ellie route to get her excited reaction to Dylan being sent away. You can have 0 Ellie points, be on the GW, Sam route, or have the maximum Dylan points you need on the Dylan/Amber route
So Ellie doesn't care if the entire neighbourhood sees her naked, as long as Dylan isn't there. Sam, Julia (even without knowing her crush on Ellie), Neil, Amber, Sophia, Liam, complete strangers, doesn't matter. Just not Dylan. Really curious as to what he did to provoke that response