I don't think Sia needs to be replaced. After all, we look for both beauty and brains(in this case, good acting) when we see a serial. So, even if Sia falls short in beauty, i think she is really doing a good job in her acting department. She emotes really well and this for a newcomer is very difficult. To tell you more, this might have been the reason why Abbas Khan was replaced by Vishal Singh as Abbas emoted really pathetically.
As far as Sia goes, i love the way she smiles. She really looks cute when she pins her hair up and leaves her hair. I do not see her irritating at all. Infact, i love her acting and emoting skills.
To me, its just not beauty that matters. But, again, as i say, we live in a democratic world, so all have a right to express what tey feel. So please do not take this reply of mine as personal....This is just my thought on Sia, the character....