To be fair, that's just Ruby's speculation regarding what happened to her mom. In the series, we've only been fed about what possibly happened to Summer. The only real info we have is that she went missing and that the series has been careful to not use the word "dead" or "died" or "death." When Yang first talks about Summer to Blake back in Volume 2, she just says she was "gone." So it's something interesting to ponder. But so far nothing confirmed yet.
To be fair, that's just Ruby's speculation regarding what happened to her mom. In the series, we've only been fed about what possibly happened to Summer. The only real info we have is that she went missing and that the series has been careful to not use the word "dead" or "died" or "death." When Yang first talks about Summer to Blake back in Volume 2, she just says she was "gone." So it's something interesting to ponder. But so far nothing confirmed yet.