98% sure it's Pari. She has ring on the same finger, you can see a fleeting glimpse of of it when 'ahana' gives naren his pizza. Plus same length hair and what I thought was the same walk as Pari.
They've given us clues since the leap started: Pari does not cook anymore which we could assume means has something to do with a negative experience in her life connected to food/restaurant and love interest. She doesn't like being in crowds, you see her spending most of her time in the dark. She 'loved' someone but we do not know anything apart from his name 'aman' but did she leave him or he leave her?
I think she must have been ok to fall in love, wanting to give a man a chance, but naren must have assumed she died and left her, which is why her anger against her father and men in general grew ten fold, she must have thought naren was different but turned out to be the same as her father, even though we know otherwise.
Ahana never said 'I love you' but naren said you could see it in her eyes. Pia is a very expressive girl but Pari isn't, she wouldn't have said I love you straight away but many times you can see what's going on by the look on her face. Naren and ahana's relationship was probably still in the friendship territory but if not for the accident was most probably about to get serious with the proposal.
It's likely if ahana is Pari that she might have said no to naren anyway even if she loved him, because of her parents broken marriage at the time.