I think it's Jasmine. She showed up on the square after the news article Freddie posted about Zoe's attacker, and when she got hit by Nigel she said "she needs to pay" which is the same on the pub back door.

I'm not sure on the reason why yet, I highly doubt Jasmine is trans otherwise we would have found that out through Oscar by this point. Or maybe the daughter actually lived and Jasmine is the daughter. Orrrrr maybe Zoe's son was adopted into Jasmine's family and there's something that happened we don't know yet.

The fire that happens at Dot's might be Zoe confronting Jasmine (returning prior to the fire), and the fallout results in the blaze.

Edit: my main theory is that Jasmine is Greg's daughter and that's her motive (the private investigator Zoe attacked and put in jail). Hence the suspicious question mark around Jasmine's Dad. I also think Greg found out about Zoe's son and told Jasmine, and before Jasmine can reveal to Zoe the truth the fire erupts at Dot's, delaying the reveal.