If I had the option of going back or taking my sister to a new world I think I'd go with the latter. Doing so might make her happier.

[Despite all the haunting hallucinations... after a couple rounds of trading (though still with a bit of Meri in her) she finds herself calmed with the idea. Of taking her sister to a new world where her body won't be so corrupted. Where those worms won't be writhing under her skin and Grail wouldn't be tempting her with its vile words.]