Should I commit to 5 days on the Appalachian trail?

My sister has decided that she’s going to get into shape by doing 2 weeks on the AP in the Shenandoah Valley area (Front Royal to Waynesboro) this fall. I think she’s got it backwards – you get in shape first, and then you hike the trail. She’s asked me to do a 5 day stretch with her, and I’d love to, but I don’t see how I can get in enough training between now and the end of September (I’m sadly out of shape). I have access to ultralight camping and hiking equipment. Would it be dangerous to go unprepared?