If I remember correctly from Onegai Teacher back there she did say something about being absent for 18 years, it could mean that after these events she will go into that comma state again, from what I remember that condition affects the victim in such way that it literally stays unchanged, doesn't age or anything. In Onegai Teacher she and the MC have the same condition and it seems to be having something to do with some event or incident. They simply stop.
If we are correct about this being a prequel, and we most likely are because everything seems to fit like a glove, during the next few episodes we will learn pretty much everything.
Although this could very well be a long distance sequel. Beats me, R/Lemon remaining a loli is a good thing in overall but it's pretty damn sad that the condition is sudden and can happen at any time on random. I wonder if they will show her collapse in a stop for a bit soon.