It doesnt sound like IBD to me bc i know its more common in boas and bc i thought it settled in and the snake deteriorated pretty quickly. 8 months seems like an awfully long time for her to have it. Im far from an expert on it though.
Did you contact the person you bought her from asking if theres something that you are doing differently that could be making her wobble worse? (i.e. like stressing her out more?)