I would contact your case manger or whoever you main point of contact is for the services she's getting now. Some of the confusion may just be a matter of semantics. Not every child with developmental delays has autism but every child with autism has developmental delays. And not every child with autism has been given an official diagnosis. They may just use that term because it's a bigger bucket, so to speak.
Call and ask all your questions, hopefully they can help calm some of your anxiety. If not, look online and find an educational advocate in your area and they can help you navigate through this.
It's all pretty confusing and some school districts don't do a good job of helping make it easier for the parents. Just ask questions and keep asking!

My son was diagnosed PDD-NOS a few months before turning 3. The diagnosis was made by a Developmental Pediatrician, but that in and of itself did not get him the services he needed in the public school. We had a neuropsychological evaluation done which made all the difference with his school. Once they had those results, they gave him all the services recommended by the doctor who evaluated him. It is a very expensive examination but I believe most insurance policies covers at least part of the cost. My son's school actually picked up the entire cost. Something to think about.

Don't forget that if you disagree with the results of the district evaluation, you have the legal right under IDEA to an independent evaluation at the district's expense.

The school is going to want to do their own evaluation even if you have there DX because they want to find out what the child's abilities are academically. Second to that they do not want to have to pay for therapies they do not have to. I know it is very frustrating but just have whatever testing done they ask for because if your child really needs certain therapies you will use that information against them.

Just do not let them push you around, fight for what your child needs and do not take no for an answer

I strongly recommend reading the Nolo Guide to IEP's by Lawrence Siegel. A medical diagnosis of autism does not guarantee an "educational" diagnosis but having the medical diagnosis will strengthen your case if your district tries to deny services and you have to go to due process.