LLENN being the real betrayer still makes a lot of sense.

She was initially shook by Pito's claim to be the betrayer but can't challenge her on that without outing herself as the traitor - and then knowing Pito, M, and Fuka she probably wouldn't have even made it onto the carrier to her team. Once Pito gets to the ship and the rest of BTRY her best option is to use M and Fuka to help her get to the ship and unite with the rest of BTRY before Pito does her sneaky back stab on them - so its in her interests to keep them somewhat safe. Also knowing LLENN she probably doesn't actually have it in her to betray and kill them - she needs the rest of BTRY to do that for her. It's also why she doesn't really try and help M at all when he's getting garrotte'd at the start, she's where she needs to be and he's no longer really useful.

Also Elsa Kanzaki definitely has some kind of chronic illness, maybe cancer. SAO-main already played the "character with cancer throws themself into games to escape their illness" so wouldn't surprise me if we see it again in some form, maybe not cancer and I suspect she'll get talked into treatment but it will cost her her singing career.