I don't think it's too out of line for Applebee's to have fired the server over what she did. She took a customer's receipt and signature and posted it online and while the data on the receipt won't likely lead to any problems (beyond the PR ones) for the customer or for Applebee's it shows a lack of judgment on the part of the server. I don't think I, personally, would have fired someone maybe gave them a talking to and a write-up but that's how I'd roll A firing still wasn't too out of line.
All said, what the pastor did was a huge dose of assholery and maybe "deserves" being called out on it.