OP, this all sound very tough. I have taught in secondary schools who are able to accomadate students with severe physical needs, for some of those students I do think it is the right thing to be in mainstream. They all had at least 1:1 though, in some cases 2:1 support (which is possible, no matter how much your LA may pretend it isn't).
You mention that the secondaries do 1:1 differently, and I just wondered what you meant by this? If it's that the 1:1 isn't always the same person for every session, I would actually see this as an overall positive- your daughter will develop relationships with more staff members, and so will be better supported if there's e.g. staff absence etc. Don't forget many secondaries have slightly longer days, so TAs have to have a break in their day by law too. In schools I have worked in, children like your daughter with physical/health needs were always prioritised for support if there was staff absence, and I do think their needs were met. Some of them did thrive in mainstream, and it may surprise you how inclusive peers can be, even if an adult has to always be present!
I fully appreciate it's a really scary transition, but I would at least speak to the allocated school, and see what their plans are. If you think those are unsuitable, then obviously do push for the special school!
I'm not saying the LA or the school are right, by the way, and I know equally sometimes schools are pressured to say they can meet needs, even when they can't, or things get lost in translation. It does all sound like a complete mess, and if the 1:1 has been removed from the EHCP then that is a major issue- I do think if they wanted mainstream, I would consider pushing for 2:1 at key times.