For Elain supposedly being sweet and kind, she sure rage-baited Nesta and then turned around and victimized herself.
First of all, Elain had no right to just show up in the HoW without Nesta's consent.
Then she started off their conversation with, "Are you enjoying your time up here?" Nesta's not on a vacation, Elain. She's locked up in a cage. Elain is so dense. Could you imagine if someone had asked Feyre if she enjoyed her time in the Spring Court manor after she had been locked up? Feyre probably would have punched said person in their face.
Nesta, justifiably, responds with, "I don't have any choice but to be here, so I don't see how I could be enjoying myself." Nesta calmly expressed to Elain how she was feeling about receiving the Tamlin Treatment.
Elain continued to rage-bait Nesta with, "I know the circumstances for your coming here were awful, Nesta, but it doesn't mean you need to be so miserable about it." Nesta wasn't being miserable. She simply stated her feelings, and Elain decided to make it all about her. If anything, Elain was being the miserable and insufferable one.
Elain then proceeded to act like she's better than Nesta because she handled her trauma differently.
Nesta, once again, opened up about how Elain, Feyre, and Rhys had hurt her feelings. "For packing my things while Rhysand and Feyre told me I'm a worthless pile of shit? Yes."
Then Elain, once again, makes Nesta's feelings and Nesta's imprisonment all about her: "Feyre warned me this might happen." Yet another rage-baiting line on Elain's part. This should have been Elain's opportunity to tell Nesta that they loved her and were trying to help her, but no, she made Nesta's feelings all about her rather than re-affirming to Nesta that they love her. If the takeaway message from an intervention is that the person feels ganged up on and feels like everyone thinks they're a worthless pile of shit, then the intervention was a complete failure. Elain doesn't even apologize or own up to it and instead places the blame on Nesta.
And then Elain's parting rage-bait: "Cassian said he thought the training was helping." It's been two weeks. Nesta's rage isn't just going to go away overnight. She's not going to heal from twenty-five years of trauma in two weeks. Especially not when her cruel and manipulative little sister comes over for the sole purpose of baiting Nesta into a rage.
Elain left crying, trying to play the victim, but she was the aggressor. If anything, Nesta was Elain's victim. Both sisters had their feelings hurt. Just because Elain's hurt feelings show via tears and Nesta's hurt feelings show via her raging, does not make Elain's feelings more valid than Nesta's. Elain spent that entire conversation talking down to Nesta and invalidating her feelings; she had no right to leave and play the victim.