Hi Sandie, there are different views regarding SN provision. Some people hold the view that Mainstream education is every child's right, so it is the LA's responsibility to provide anything that would make that possible. They are right. (The test is whether the provision is compatible with efficient education of other children). Other people think that Specialist schools are the best place for some children with SN.
The thing to be aware of is that the two types of school will approach the same need in different ways.
Mainstream schools will generally provide extra adult assistance, from a Teaching assistant, to supplement the teaching in the classroom. SALT work is normally provided as an 'extra', whereby the child is withdrawn from part of the day to do some specific activities.
Special schools often have a 'whole school curriculum' for their SALT work. In other words, the SALT work is woven into all parts of the day. For example, in DD1's school, Makaton is used at all times alongside speech, by the teaching staff, support staff, and receptionists, etc. The SALTs do 'language groups' at set times, then the teaching staff continue the focussed elements throughout the school day.
Your question was "does he have the powers to MAKE her move schools or is there something else that he should be trying in order to help the school meet her needs?"
My answer would be 'don't think this is a negative thing until you have seen all the schools available'.
Special school places are rare as hen's teeth. If you are being told that your school would support your DD's move to one, it really is worth investigating.