Let's rewind back to pre-Yuv and pre-Kanaiya and pre-rape. The family, actually Kul, had a problem with their lifestyle. But that's really it. Raghav was an issue, but nothing horribly major. All four were good daughters, but in different ways.
Now Tanya unfortunately goes through a rape. Everything changes for the people "in the know": Kul, Yuv, and Tanya. Trishna has NO idea what's going on. Her world was the same as before the rape. She's thinking about marrying Yuv. So because she's not understanding Tanya's tears or noone including Tanya has divulged anything, Trish hence is selfish? Huh?
You propose that Tanya is the unselfish one because she did all this (marry Yuv, keep everything a secret, "sacrifice") to preserve the honor of the family, first and foremost. Yes, I agree that that is an unselfish act. Her "unselfishness" stems from her reaction to her rape and its implications (protecting family's honor).
Now to be fair, Trish never went through the trauma of a rape, nor was she included in the discussions about her sister Tanya--most importantly, she was not in a position that she had to preserve her family's honor. Hell, she doesn't even know about Tanya's rape. She knows nothing.
Let me ask you one question: If Tanya was NOT raped and fell in love with some guy and life went on, do you think she'd be that much different than Trish? Or Sujata? Or Manshaa? You don't think Tanya would place a lot of importance to the guy she wanted to marry? Or think about herself? Is Sujata selfish because she thinks of Raghav and herself much of the time?
EVENTS and SITUATIONS and CONTEXTS demonstrate whether you are selfish or not. If those very same events or situations did not happen to another person or shared with another person, why is that person she criticized? Should Trish have been raped so that we can see if she's selfish or unselfish? I bet you that she would have done similar to Tanya. Kul would have made sure of it.
Correct me if I am wrong, but Trishna clearly was not criticized much in this forum much prior to the Tanya rape/marriage. It's perfectly acceptable to praise and respect Tanya for her "sacrifice" which by the way includes her sister too. But this does not make Trishna selfish (selfish with regard to Deep? no.). Selfish is when you take something from someone else, KNOWING AND HAVING PERFECT INFORMATION. Trish did not have this.