Hi DS,
It is good to hear from you...though sorry it is due to increased anxiety at this time. :(
I understand how you feel...as interpersonal issues are a trigger for me as well.
Preparing yourself with some empowering and positive mantras as you get ready to attend the birthday will help. Speaking words of affirmation will lower your anxiety and give you the ability...to if not enjoy...at least get through the event. Below is a link with examples of mantras for you:
anxietynetwork.com/content/coping-statements-anxiety...and who knows...you may actually end up having a good time! Remember the time previously when you were nervous to go to a family get together...
...and you stayed longer than you anticipated because it was going so well. :)
You can do this...and it will be a gift to your husband to step out if your comfort zone, and attend his niece's party.
I am sending encouragement your way!
S.C