I think things are usually simpler than we make them out to be. We know for certain that SM and the friend were discussing an upcoming wedding.
What about if the friend wanted to order some fabric and they spent hours online together Saturday -- viewing and texting. A short while later, the friend takes a vote from the wedding party, a decision finally made, and the friend asks SM how much fabric to order, and SM never responds.
IMO, I think I would also categorize this as an abrupt ending.
SM went dark. She never heard from her again.
How could this not be a gigantic RED flag?