mummyloveslucy, I am going to be blunt, because I care, so please don't think I am being harsh; I know how hard it is to see your child struggle and be different (DD1 has GDD). So:
A 1.5-2 year delay at the age of 5 is not 'mild'. Would you put a child who has just reached preschool age into a reception class and expect them to get on with it? No. Would you expect a just-turned-2-year-old to behave in the same way and cope with the same activities as a preschooler? No. Anyone who is describing a 1.5-2 year delay at the age of 5 as mild is doing your DD an injustice, IMVHO. She clearly has significant needs.
Your DD is at a school where she has no access to additional support, no access to an ed psych, and no access to SALT. She doesn't have a statement of educational need. Does she even have an IEP?
I realise that your DD has been with the same children since they were 2. And I realise the pain is huge of seeing your child peel away from those children in terms of development. I see it with my DD1, who has known some children since birth, and now is so behind and different. It hurts. But it is.
Evidence shows that the single biggest factor in future outcome is early intervention. By allowing your DD to be sidelined in her current school, and not having access to any additional support services, you are missing the opportunity to give your DD a chance to catch up and gain confidence and independence.
I think you know that repeating Reception year wouldn't benefit Lucy if it is simply repeating this year's activities, and I think you know that she will struggle massively without additional support in Year 1.
If I were you I'd be looking at the state sector to see what schools are out there, what their experience with SN are, and what they would be implementing for your DD. I would also be writing a letter to the LEA requesting a statutory assessment. I would not be allowing her to struggle any more.
No one can be certain that they have made the complete best choice for their child. But I know that the relief I feel having got a statement for DD for when she starts school is huge. I had expected a fight for provision, and thought that perhaps they would offer some 1:1 (although she would need full 1:1 is Mainstream). The LEA were fab, and offered our local Special school straight away.