I’m assuming that, when you asked your five close friends to be bridesmaids, you didn’t tell them you were “hiring” them for the position, right? You didn’t offer them a paycheck, or study their qualifications, or invite other interested candidates to submit resumes. This isn’t a job one gets hired and fired for. That said, you can tell your friend you no longer wish for her to be in your wedding. But don’t disinvite her from the wedding party unless you want your friendship to be over. It’s fine if you do want the friendship to be over. Maybe the unpaid cable bill is the latest in a string of irritations and betrayals, and you’ve simply had enough. But if this is the lone transgression in a friendship that has otherwise been unmarred, instead of “firing” anyone, I’d be much more moved to make sure everything was okay with my friend. I’d worry about what is going on in her life that she racked up a big cable bill — in my name, no less! — and left it unpaid even months after promising me she’d take care of it. If finances were that much of a problem for my friend, I would probably eat the cost of the bill and either volunteer to pay for her bridesmaid dress (and related costs) or gently suggest she take an honorary role with fewer associated costs, like keeper of the guest book or reader of a favorite poem.
Bottom line: If this is solely about $900 and the fact that your friend broke a promise to take care of the bill, then I’m not sure that’s worth ending a friendship over. If the unpaid bill is par for the course and only the latest in a series of thoughtless and selfish acts, then consider this an opportunity to end a friendship that no longer fulfills you.
If you have a relationship/dating question I can help answer, you can send me your letters at firstname.lastname@example.org.