I didn't think I was going to like Cole, but he won me over, so I feel for him...but there's a strong possibility that Sera spent at least some time in Ferelden Horror Story: MURDER ORPHANAGE, when she was in the Denerim Alienage, so if that's where her fear of demons comes from, can you blame her?
The Denerim alienage orphanage is one of the saddest and most chilling things to me from the first game.
I think she would have spent some time there but it didn't seem like she lived there long before getting adopted by Lady Emmald.
Interestingly, Sera does have some negative comments about the people in the Alienage (and the tree ofc xd). Not everyone in the Denerim Alienage is equal. I got the impression that the Tabris family was relatively well off as Alienage standards go...they have a decent home and the CE's father is apparently better off than most as he can find you a really nice groom/bride.
Then there are the elves that beg in the streets. I would imagine those living in the orphanage are at the bottom of that society and most likely turn to crime and/or meet a violent end. That's not even mentioning the demon stuff at the Denerim Alienage lol. With that in mind, it makes sense that Sera would have resentment towards the place.
Funny enough, my Surana Warden headcanon is that she was born in the Denerim Alienage before getting sent to the Circle. I doubt she knew Sera though.