I have 2 LTE phones, one on ATT and one on VZW...both get great reception (full bars) at ATL airport....neither gets great data speeds (to the point that it's a huge drain on the batteries and impossible to do anything involving data)......I've always assumed both ATT & VZW circuits from the towers are maxed but who knows I guess (I'm sure if I asked a front line associate in the airport someone would tell me they want me to use the airports wifi service too)

Personally I highly doubt Marriott would be blocking anything after losing the case with the FCC

I'm more inclined to blame this on Verizon than Marriott...but in any case, file a complaint with the FCC: https://consumercomplaints.fcc.gov/hc/en-us

Let them & their field agents bring out the monitoring equipment and figure out what really happened.

At the very least it'll stop the field agents from harassing little Mom & Pop hotels over their cable TV systems' spurious emissions, which they've been doing a lot of lately.

Some MiFi models will act like a USB to Ethernet adapter when plugged into a computer. Next time she gets 0 throughput with WiFi, give this a shot. If nothing else it will definitively rule Verizon out and let her get work done. It might also be worthwhile to upgrade to a MiFi model that can support 5GHz (for example, the 6620L); 2.4GHz can be extremely crowded depending on the property.