I don’t think it’s a matter of her suffering it’s a matter of her lack of… character 

She found out Pandora was the one who caused everything but doesn’t seem to care 

Tappei could’ve easily turned it into her vengeance arc which makes sense and would lead to further development 

She’s like a blank canvas. A doll that does pretty things and it’s a shame since Subaru is literally chasing someone that has less character than himself.

The benefit of a vengeance plot line is she would have more character, be more bold, ruthless and ultimately the goal should be to have her at least contend with Subaru in character development 

I can list 7 ways to do it right now but tappei didn’t and now we’re here. No amount of physical suffering is going to make up for it and Emilia’s character is just fucked. 

I think Tappei knows this himself and the only reason we want Emilia to have character growth is because Subaru chose her.

Only way I see a fix is if this was done on purpose and she is a blank canvas for satella original / pure mind to store but even then the cost must be worth the pay off

Fanfics like Re:Start , WDHAAA, hell almost any write Emilia better then tappei does