I'd be cautious jumping to "what's wrong" and then guess treating. Sometimes it's difficult, but hands off and allowing nature to take its course has always been a good rule I learned years ago. Especially young pullets just coming into point of lay - there are all kinds of things that happen with those first eggs and it make take time to work it all out. Just this season I had a large dual purpose pullet lay dble eggs every day. Then after what seemed nearly a month, she skipped a couple days and was clockwork egg production after than. Another large dual purpose pullet started laying at 20 weeks in spite of point of lay being 23-24 wks and sometimes longer. I figured she was early Apr spring hatch which may have an impact on sun hrs in July that were reduced by many days of overcast skies with low lumens. The Rooster had been breeding her, she submitted no problems and he's a gentle big guy. She was laying consistently every day for nearly a week. Then she skipped a day. On that day I noticed she was scratching around quite a bit and thought it a little odd. Went into the house came out a couple hrs later and she was dead. I processed her and saw that an elongated shaped egg was sideways in the oviduct. Egg bound into her body cavity. That type of situation usually causes death because the fecal waste backs up (uses same path as oviduct) and the chicken dies of sepsis. Things just happen when you raise animals. Keep making notes, be observant but please give that little girl some time to iron out her cycles. Unless she shows signs associated with illness or physical issues, I'd be tempted to just observe and not disrupt a digestive system with ACV or OTC medications.