Just now I make a test.
Create two user forms : uf1 and uf2.
I make "Show Modal" to false on each user form property.
In uf1 I put two checkbox : cb1 and cb2.
In uf2 I put one label : Label1
Then I open both of the user forms.
Tick the cb1 in uf1, the Label1 shows in uf2
Untick the cb1, The Label1 is hidden in uf2.

If that's what you mean, the code is like this :
Sub in uf1
Private Sub cb1_Click()
If cb1 = True Then uf2.Label1.Visible = True Else uf2.Label1.Visible = False
End Sub
Sub in uf2
Private Sub UserForm_Initialize()
Label1.Visible = False
End Sub
Please note that the code in uf1 doesn't do error checking, for example : if uf2 is not exist (not showing) then .....