Every lease has an implied covenant of what we call quiet enjoyment and habitability. It sounds as if these covenants have been broken, which would free you from the lease. As a practical matter, you will likely have to move before you get the deposit back since she may fight it. So first ask yourself can you do that? Getting out ASAP would be best for your own sanity and health. Second, to prepare for any court fight, document the problem - have copies of the extermination bills and take photographs of bites and of fleas if you can get such a photograph. Next, whether you move out immediately or not, 1) telling her she has violated the lease by breaching the covenats of habitability and quiet enjoyment, 2) demanding return of your deposit and 3) demanding damages for your bed. Give her 30 days. If no response, then proceed to small claims court. You might not prevail regarding the bed, but go for it. In the interim, also immediately report the situation to your local board of health or other public health official. They may able to come down on her and be a strong ally. If she tries to evict you for doing that, then she is subject to a retaliation claim by you. Good luck!
To questioners from West Virginia & New York: Although I am licensed to practice in your state, I practice on a day-to-day basis in Massachusetts. I answer questions in your state in areas of the law in which I practice, and in which I feel comfortable trying to offer you assistance based on my knowledge of specific statutes in your state and/or general principles applicable in all states. It is always best, however, to work with attorneys and court personnel in your own area to deal with specific problems and factual situations.