If she is connected to WiFi and has the symbol attached next to the WiFi symbol (WiFi calling/vowifi), she can receive and make calls using our local SA rates.
Best she confirms with vodacom but this is how vowifi works for our networks.
US's networks from what I read are the biggest pains.. so I honestly think its a US issue. Have you tried any other SA sim on the phone?
I think t mobile is the most chill if you haven't tried them already
Its possible, Xiaomi had a similar one one of the previous years only not blatant like Huawei.
You had to buy a certain combo of things that gave you a similar discount as per this Huawei one.
Someone (or maybe a few- can't recall) here actually snagged that deal.