Just curious but do you think Eleanor knew about Chuck trading Blair for a hotel? Or any of the other abuse Blair suffered from Chuck? I’m wondering for a fic.
I don't see Blair as telling her mother, tbh! She might know in the way that everyone knows, through GG, therefore maybe not understanding the severity of it, or how much it impacted Blair? But this is my headcanon. Canonically, I don't think we see anything.
That said, for all her flaws, I don't think Eleanor would've endorsed the chair wedding the way she did if she knew exactly how that guy was treating her daughter.
At some point, everyone seems to know about the hotel thing, inferenced by how it's brought up by people who Blair didn't tell, which implies that these things are common knowledge. That said, nothing Gossip Girl really brings out seems sincere or from a place of concern, more like mockery or ruthless cruelty about everything - so if GG really brought that news out, it would've been heavily trivilaised.
Would Eleanor have taken a GG blast about all this seriously, especially if her own daughter never said a word to her? I'm inclined to believe she wouldn't think it was a big deal if the only info she had was a gossip girl blast, which... i think might have been the case.
Again, these are all my headcanons and mine alone, feel free to characterise and do whatever feels true to you in your fic! good luck writing :D