MDI parent MDI child issue

[C# Programming]

Hi I have an app with its main form MAIN which is an mdi container.
One of the options from this MAIN is to show a database record in a
new dialog (DIALOG_A).
This new dialog is a mdi child and its mdiparent is MAIN.
Now another operation that MAIN can perform is to create another new
dialog (DIALOG_B).
This also is a child mdi and its mdiparent is MAIN.
However, from DIALOG_B .... i would like to call DIALOG_A also.
I am getting problems however becuause Dialog_A is not an MDI
container.
Could some one suggest some help.
Thank you very much.