OP you have no idea what she may have been through, how hard her life is behind closed doors, or how long her contentment will last.
Many people's lives look wonderful from a distance, but everyone has their fair share of disappointments, worries, setbacks and all the rest, she may not advertise it, but they will be there, she is human.
We have to be happy for the moments and times when things are going well for us or for our friends. A true friend would be really chuffed for her, and you do not sound as if you have her best interests at heart.
Your friend is lucky to be enjoying what I would call golden times, when all is well, be happy for her.