I do t think ishita should be blamed here I mean u say that Ishita praises Mani but there is nothing wrong in that it's not like she is doing all that on purpose to gain some sadistic pleasure while watching Raman suffer she does it because Mani appreciates her and makes her smile something that a friend would do and I personally dont read anything more in that relationship then friendship so I think we should not worry.
And coming to Raman yes I feel bad my heart goes out to him when i see him suffer but you have to agree he taunts ishita makes fun of her figure her heritage and makes fun of her every chance he gets though I love the nokh-jokh in there relationship Raman takes it 1 step to far. All a women wants is to be appreciated and Raman doesn't give her that though we have never seen Ishita affected by all these taunts i do believe deep down her self esteem is getting hurt.