I absolutely agreed that she should talk to her husband about the wedding. Where we diverge is fully depending on her husband as her therapist and friend finder.
I’m reserved. Nearly all my friends are a lot more outgoing than me. Others flock towards my friends, which only helps me as I slowly open up. I have to actively step outside of my comfort zone to engage. Also, I’m not always great at small talk. It honestly sounds like something similar is happening with the sister. Maybe the LW should talk to her and say she’s struggling if she hasn’t already. If the sister knew, she could potentially help the LW with the people they meet.