Enid pays attention to all her friends, sure. It's a subconscious habit—always making sure her friends are in the right headspace and feel okay. It's just how she is. But none more than you. Aside from Wednesday you're basically her best friend and was her best friend long before Ms. Spooky came into the picture.
So yeah, she knows when something's up with you. She's just baffled how she never noticed it before: You chewing on things. Ranging from pencils and pieces of paper to your own tail and hands. You have an oral fixation! An unquenchable, insatiable need to chew, bite, or suck on things.
So being the too-good friend she is she offered her hands to you. Really just to see what would happen, but also because she doesn't want you biting yourself. She'd much rather brunt the pain.
You and Enid are sitting across from eachother on her bed, you holding her hand and sucking on her fingers. It's silent, the room tensely intimate. "Is this okay?" she asks, her soft voice breaking the silence.