My daughter was recently engaged and we couldn't be happier.  
[Edited to reflect my sincere and true feelings.]
The take away message:
1.  Ask daughter if she wanted my help and if she did, how would she like me to help.
2.  Throw all expectations of what I perceived my role as the mother of the bride to be out the window.  
3.   Ask myself first if my "helpful advice" is truly helpful at all.  Ask  myself if it comes across as advice, criticism, or my agenda.   
4.  Be thankful and praise often.  
5.  Love unconditionally.