Maybe time to suggest (concerned and lovingly to all the three of the family) that an arbitator maybe a family doctor or child specialist. advise what is best for little A.who has indeed been fostered and seperated from that home unit for a large part of her little life.
do this officialy so notes are taken and kept.
maybe your son could be advised you are doing this for A's good and for the reason...do this before A shows seperation anxiety symptoms.wet beds etc..
My bet is she is ...and sooner rather than later.
A voice on the phone is not enough...nor a letter she cannot not yet read.
also you could start a diary..later she will read it will you..and see in retrospect your love..sorrow and how disempowered you are.For now.

is there a church connection..the wife may listen to a pastor.Still back it up with paper work.
Any educated child worker would recommend a secure transition for A.This did not happen and as this couple settle again together they would benifit from time alone and A. being safely with you.

Also do keep doing things for you...massage..even if you cry (cathartic) and sailing..WOW.
The important lady is A. The important time is soon.

Taking a whole differnt stance...The wife will still be coming down to Planet Earth since the Games.Adjusting to home life.May have regrets at her abscence from A. May be so angry at herself that she is not rational.Could be turning that wrongly into hostility toward you.So much for her to unravel.
So I think you are right to be concerned.
Love Mountain ash