Hi there, big hugs for you!
Could be pain. 2yr old molars are HORRID - Owen got them around 16m - he got all 8 molars then. The molars refer pain to the ears, and it becomes worse at night and when they lay flat. I'm thinking some baby motrin or whatever you doctor rec for pain 30m before bed may be a good place to start. These teeth can start to hurt well before you actually see anything in the mouth. They can also, push up and hurt and then stop for a few weeks.
Could she have an ear infection? Sometimes ear infections make us dizzy and nauseous when we lay flat. Some babies will even vomit. They also feel niggly during the daytime. Honestly I say any drastic change in behavior like this is worth a doctors visit.
Anything new in the family, new pet, recently moved, illness in the family, did you go back to work, change in jobs with someone in the family? Anything new? Changed her room around, new sheets, new curtains? Has she been ill recently, fall out of the crib, throw up in the crib, have something traumatic happen in her bedroom? How was she sleeping before this change? Was she able to put her self to sleep without issue?
Did this begin shortly after dropping her nap? Can you post your routine for us to see?
Of course this is only my opinion but... Honestly, I really don't think leaving her alone to scream and cry is appropriate if she is afraid and needing you, or if you suspect pain or discomfort. I'm afraid she will begin to feel abandoned and it will make everything worse. I would first take her to the pedi and have her ears checked. Try the pain meds and see if that helps - 30m before sleep. If it's not her teeth or ears or something medical, then I would try WI/WO as suggested, or gradual withdrawal (links to both in the FAQ section).
Try to look for the why, most often there is a reason for sudden changes in behavior. HUGS HUGS HUGS, it'll work out..