Concern about a friend after the wedding

Hi all, apologies in advance if this is a complex post! I am having a major post-wedding friendship issue and wondered if anyone else has experienced a similar thing and could offer some advice for how to handle it. I got married about six months ago and I am lucky enough to still have a very close friendship group with 4 other women I've known since we were 11. They were all involved in my wedding party and were great in helping me to get organised and stay calm on the big day. However within 24 hours of the wedding, one of my friends seemed to change. She had a few too many drinks at the wedding and left quite early, which I was a little upset about given she was in my bridal party but ultimately it wasn't a problem and I have never "told her off" for it. I get these things happen in the excitement of a wedding day! But she herself just seemed to stop talking to me altogether. I sent messages to the group the next day thanking everyone for coming and asking if they had fun and she was the only one not to reply. I sent flowers and a thank you card with a long message in it expressing how much she means to me and how glad I was that she was in my bridal party and I didn't so much as get a message to acknowledge it. I eventually contacted her to ask if she received it and I got a blunt reply back saying yes but she has been too busy to reply. However it isn't just me who is being ignored, the other three members of our group are experiencing the same. Another of the women in our social circle is getting married next year and she has so far failed to acknowledge it, despite being sent a save the date and being invited to the hen do. She hasn't even said she isn't coming to the hen do, she just hasn't replied (it has been 2 months since the invites were sent out). I am very upset and confused, and angry as I feel like I "wasted" a role in my wedding on this person for them to just cut me off. And I am upset for my friend who is due to marry as she just doesn't understand how a friend of 20 years can't be happy for her. To give a little more context, this person is still single whilst the rest of us are all married (or about to be) so we have speculated that maybe she feels left out. But she has never raised this with us so we can't be sure. And nothing has really changed in our social lives, none of us have kids yet, we have just committed to our long term partners with an expensive party! Any tips? I can't decide if I should just cut my losses and end this friendship - though we have never fallen out in 20 years until now - or try to reach out some more. Advice would be appreciated!