Grounds for SA
SOS SEN say the legal criterion for statutory assessment is that the local authority should believe that the child in question probably has SEN, and that the authority needs to determine that child?s special educational provision by making a statement.
The evidence for this is usually that they are not making sufficient progress despite the help given. Or that the help is working, but it can only be continued with provision of a statement. Which is hard to prove. That said, being placed in an assessment unit is good evidence that "the child in question probably has SEN". So you're only looking at arguing "that the authority needs to determine that child?s special educational provision by making a statement".
She will still need additional support when she leaves there especially if they decide to send her to mainstream There is some support available directly in mainstream on 'school action plus' so for a statement you need to prove she needs lots of help/ expensive help/ complicated help.
Should I request another ed psyc report now No, they'll come when they're ready, very possibly to help see whether to agree SA or not.
targets for her re: social interaction, communication and play & imagination Were the targets relevant? Did they cover all her areas of need? Does she have an IEP? Have the targets been met?
in an assessment unit for 2 terms Do you mean till Christmas 2013? 'She's in a temporary placement, and only a SA can determine the full extent of her needs' might be worth a try. It takes 6w + summer holidays for them to say 'No' to SA anyway. Up to 8 weeks to decide whether to appeal, then up to 20 weeks till you get to tribunal. In all honesty, what you do at home might well be of more educational value than anything the LA can offer anyway, statement or no statement. But having seen the ed psych, social-communication-play-imagination targets set, and getting an assessment placement do sound like good signs.