A curse is placed on Gwendolen, and why the accusation is not fair

Just like that Gwendolen  marries Grandcourt and her married life is off to a horrible start - of course the relationship right from the beginning seems cold, without love or passion, and with Gwendolen already feeling indebted to Grandcourt for pulling her family out of poverty. Then, she gets a letter hand-delivered from Mrs. Gresher - Grandcourt's one-time mistress (and perhaps the mother of his children? That part isn't clear to me - have to go back and re-read); she's returning to Grandcourt a set of diamonds he'd left with her, as promised - her one demand was that she be able to present the diamonds directly to Gwendolen: but she does so with a curse, berating Gwendolen for breaking a promise and letting Grandcourt know that she had met secretly w/ Mrs. Gresher. Gwendolen breaks down into hysterical screaming after reading the letter and its curse; Grandcourt rushes in, end of chapter. Yes, Grandcourt is a totally unsympathetic character and Gwendolen herself, though admirable, is not necessarily someone you'd like to know - this is the nature of a "round" character, not a type or stereotype - but what about Mrs. Gresher (too many G names!): she's not very sympathetic herself, despite the hardships she's endured. Her demand - that Gwendolen never reveal that they'd met - is completely unrealistic; obviously Gwendolen will have to check out the story that Mrs. G tells her: is Grandcourt a cad and a liar, or is this a set-up? (I thought it was - but turns out to be true at least in part.) She's in a position a little like Hamlet - trying to ascertain the veracity of a terrible tale, while not tipping her hand. That's really impossible to do; of course she will tell Grandcourt or ask about this alleged relationship (whether he lies, too, or not - that seems to be immaterial, in her rush to secure her finances and, she thinks, her independence). Meanwhile, Deronda, still enamored w/ Mirah, though he seems to have spent no time with her, is learning all he can about Judaism - that should be interesting, unless Eliot, as I've been forewarned, lets her novel drift into polemics.