You say that you have talked with school staff, but you don't say what your daughter's reasons are for her truancy. Why is she refusing to go to school? Talk with her. Find out. If her explanations are reasonable, try to work out a compromise. Has she missed so much school that no longer feels left out, like she no longer belongs there? If so, ask whether the school would permit her to attend for a half-day schedule until she feels more comfortable.
Another real key is what she does when she stays home. Is she permitted to watch TV, call friends, shop, sleep, etc.? In other words, is she getting rewarded for staying home? You might want to take some of these actions if she refuses to go to school: Lock her out of the house, take her to work with you, and make her sit all day in one place. Call the police/truant officer and have them pick her up for truancy. If you contact a police/school resource officer ahead of time, they will often talk with children about the possible outcomes of continued truancy. Some jurisdictions will put habitual truants in detention. The latter is often a great wake up call!
Since your daughter is, at this point, out of control, I encourage you, her parents, to get involved in parenting classes of some kind for the support and ideas shared in those groups. Another resource of course is family counseling. Since your daughter is in therapy, it would be beneficial if the entire family got involved because your daughter's truancy has become everyone's problem now.