i can tell you that with mine (20 months) i could never tell if he was teething until they were through - maybe because it was my first, but i think because A. he never acted like anything was wrong, and B. he has a small narrow mouth that you can hardly see in. plus after the first time he bit me i was very careful about putting my fingers in his mouth! so i understand not being sure. one thing i would try (since you said you already tried tylenol i assume you're not opposed to "trying" something without knowing for sure what's wrong) is substitute ibuprofen for tylenol. it lasts twice as long (works better for nighttime) and reduces swelling which i don't think tylenol does. someone on here suggested it to me when my little one wasn't feeling so well, and it does do better than the tylenol - even if it doesn't work "perfectly" (i.e. for a full eight ours) at least it will work longer than the tylenol and you should get some sleep! good luck!
OH and ps, once she has had the ibuprofen, since you can't give it to her every few hours like tylenol, make sure you're reinforcing good nighttime routines, keep the lights off, don't talk to her, etc...she may be getting into the habit of waking up now. comfort her by patting her back/tummy, give her a bit of bottle if she needs it, but try not to get her up every time she wakes up and fusses. probably you're already doing that. just thought i'd mention it!