It is possible that they have had some kind of Sen diagnosed and don't want to tell anyone whcih is fine but you would have thought she wouldn't be saying what she has said to cheat the system.
If you intend to write I would write in recorded delivery.
Ask /state the following
I write in respect if my child xx dob application to x school x county, this application was submitted in accordance with the correct process and procedures for x county on x date.
On x date I was informed by admissions dept that my child was first on the waiting list.
I have not been informed of any changes to application criteria affecting my child's applications nor have I been informed that my child's place on the waiting list has changed, and I therefore have assumed My child x remains first in the waiting list. I have reconfirmed this with staff in the admissions dept on several occasions by (phone email etc and rough dates if you know them)
As per the original application my address remains no x y street, z town, AB1 23C, and is approximately (by Google maps or some other reference) x miles from xx school. We have not moved address.
My older child z and a sibling of x is already a pupil at x school. My child has no Sen and is not lac so I undertsand that normal admissions criteria apply.
I therefore assumed that my child would be first to be offered a place at x school should one arise, unless a fresh application was received from a child who has special status such as LAC or was resident at an address that was geographically closer by the standard assessment method or there was a significant change in circumstances of a child that was lower on the waiting list which affected their place such as moving closer to the school etc.
On x date I was disappointed to hear from Mrs abc who lives at a b street, z town that her child (name ) had been admitted into x school thus superseding my child on the waiting list. I do not know (unless you do) what number place this child was on the waiting list, but as my child was first I have to assume that they would have been lower, second or even lower due to the distance they live away from the school.
While I appreciate that you cannot disclose to me confidential issues in respect of the school application process undertaken by Mrs abc I am at a loss to know why her child would supersede my child x on the waiting list, as my house is closer and if all other aspects of the appreciation are identical then preference should be given to the child living nearer which is my child x.
I know Mrs abc has an older child who is also a pupil the school as do I and I have not been made aware of any changes in sibling priorities for applications. In addition I have known mrs abc since 20xx and I believe her child to be her natural child and not LAC, and I am aware that they continue to live at x a street. I know this to be a fact because ... Eg my child has gone on play dates or whatever and during my conversations Mrs abc has not indicated she has moved house recently. Mrs abc has been quite vocal about being successful in getting a place at x schoo for her child and has intimated that she has had some special knowledge of ways to beat the application process and has in some way or another manipulated her application to get her child admitted.
I would be grateful if you could review this application in comparison to mine to ensure that the correct processes and procedures have been applied in bith cases and the correct information has been supplied by Mrs abc in the application and no oversight has taken place in the award of this place to child.
I reserve the right to formally complain about the application of Mrs abc and admission of child and appeal the administration of this application process subject to your responses.