Why don't you buy her a ticket to meet you in Bangkok instead? You have more things to do and go in Bangkok versus Udon.
Nightlife in Udon only 2 big places to go, Nutty Park and Day and Night Complex. A handful of bars and discos. Shopping wise, you got to hit the local day or night markets. Ask your lady, she will know where. The biggest shopping mall is Central Plaza Udon and a few malls like IT Plaza, Landmark Plaza, Big C and Tesco Lotus.
Food, you can easily find western food due to the large farang population here. Relatively cheap with some international buffets going at as low as THB 200 at some of the restaurants.
Sight seeing would be forest temples, bronze age caves, silk crafts market and waterpark.
If you made your way to Udon, you can give me a PM. If I am free and in province, I can show you around but don't expect much.
