A friend has a caravan in the sticks. Looking at Orange and Virgin, they say only 2G available, not 3G. Could she use 2G to connect to the internet for browsing and emails? Would she need a dial-up dongle?
I don't think that there is such a thing as mobile dial-up dongle. A 3G mobile will connect at 3G if it is available or at 2G. You should be able to get internet at 2G but at a slower speed. For each mobile provider you need to look carefully at their coverage and then take some of it with a pinch of salt. Does your friend have a mobile phone? Does it work well in the caravan's location? If it doesn't a mobile dongle will not. Be wary of the costs of downloading internet data over a mobile network.
Has your friend looked at the coverage for other mobile broadband providers. I use "Three" in north Northumberland and it uses 3G. What about T-mobile wonder what their coverage is like. Best advice is to look at all the mobile providers and check their coverage.