Bless her. What help do you have at present? I assume she has an EHCP? Have you had an emergency review, with TAC meeting?
Essentially, you need to rewrite her programme of intervention to make it suitable for where she currently is, not where she used to be.
Start where she is and think about what would be the next step. She probably needs some home tuition, at a very very low expectation level initially. I have successfully used play therapists in this role. You need small amounts of time regularly - 3 half hour sessions weekly better than 1 two hour session, for example. Just get materials that she would have liked before out - playdoh, bubbles, squeezy toys, finger paints, whatever, and have the therapist play with them, inviting DD but not forcing her to join.
You need to think about her programme in relation to the preparation for adulthood areas - health, independence, community access, and education and employment. She needs a new "curriculum" or timetable based on touching each of these 4 areas in an initially very low key way over a week. For example, health and community access might be covered by going to a disability session at a soft play centre or a special needs cycling session - but the first step towards that might be, that she can sit in the garden or kitchen and listen to music/ eat a sandwich with you for 5 mins. Small steps. If she can't manage a step, make it smaller still.
You need a LA rep to support such a programme and commission a person to do the "inreach", and ideally a prof to support the recommendation - a speech therapist or EP. Who has been most helpful in the past? Contact them.
Good luck.