Bryony Cleall says she felt she had let her "nearest and dearest" down when she was not named alongside twin sister Poppy in England's World Cup squad.
But she did not make the tournament squad - and has had to watch their progress to the final from home.
"You feel like you've let them down," Cleall, who has seven caps, told BBC Sport.
"They want the best for you and you feel like you haven't done it."
Cleall, 30, said being asked by Wasps coach LJ Lewis whether she had told her parents about her omission was "the bit that sent me over the edge".
"It wasn't talking to her and telling her," she said. "It was the bit where it hits home... that was the worst bit I think."
'She cried and I cried'
Simon Middleton's squad selection prompted mixed emotions for Cleall as she was omitted but her twin sister was in the final party.
Players were given a choice of how they would find out if they had been selected or not - and Cleall asked to be told by text message.
When the message came, she called her sister, who went to her house armed with pizza, cookies and wine.
"We cuddled," Cleall said. "She cried and I cried and then she said: 'I wasn't even going to be here because I didn't think this was an eventuality.'
"We ate the pizza and cookies and drank the wine so it wasn't a bad night in the end. But that was tough. They're the toughest parts of it all. It's not even your own disappointment but people around you."
Cleall is flying out to New Zealand this week for Saturday's final against the tournament hosts - and her sister has helped pay for her flights.
She knows there will be conflicting emotions, but says she would "never miss it".
"I have never missed a moment Poppy has been on a rugby pitch," she said. "For her first cap, I flew to Italy.
"I would be lying if there aren't going to be tears for numerous different reasons. It will be such a crazy situation.
"I have never been to New Zealand, let alone Eden Park, let alone a sold-out Eden Park. It'll be incredible. I'm sure there will be a ridiculous amount of emotions."
The Cleall sisters have played together for both club - Saracens - and country but never together at a World Cup.
Cleall, who signed for Harlequins on Monday, described that as a "missing piece of the jigsaw" and said it had given her more motivation to be a part of the 2025 World Cup.
She said: "Somebody said to me the other day: 'What are you going to do?' I'm not at a crossroads as such, but I got to this year and thought: 'I wonder what I'll do. How will I set my career up after rugby as I have just turned 30?'
"I thought maybe I'd start heading towards coaching or setting up that kind of teaching career. But now I'm like: 'No. I have three more years to finish that jigsaw and finish off the memories I have with my sister.'
"It's definitely put a bit more fire in the belly and off we go for another three years."