We finally spoke to the photographer yesterday. My fiance found her on WhatsApp and sent her a message to call him - she did within 30 minutes. He explained our concerns and frustrations very clearly and let her know this level of service was not acceptable to us - or to the other brides who are waiting for their pictures. She did apologize and said she had some health issues in March/April and it has put her behind - she sounded embarrassed that brides were upset with her and asked if I had their names for her to call and apologize to them directly. She offered to let us not make any additional payments until she sends us the tracking number letting us know our photos are on their way, which is what we would have suggested anyway. She also immediately sent a follow up email to us with another apology and confirming the payment arrangement.
All in all, my preference would still be to go with the other photographer. But at this point that doesn't feel like the right thing to do. If brides had said she was unprofessional or a problem on their actual wedding day, I would in a heartbeat. But that is not the case - so I have to just let it go now and trust that it'll be fine.
I do hope I did some small benefit in telling her in a constructive way (versus coming across like a demanding bridezilla) about the abundance of concerns floating around out there about her! If she really didn't know how big of an issue this was for her clients, and now she does, perhaps she'll be more on top of it for future brides so they aren't in a complete frenzy a week before their wedding!