Yes, the train T5 leaving from Beijing has one stop at Guilin. Its terminal station is Hanoi, Thus, you can take this train.

There is a train from Beijing to Hanoi twice a week, pass Guilin, but you can not buy ticket, that's impossible! This train from Russian to Hanoi, so hard to buy ticket! Everyday have a train from Nanning to Hanoi (~~~500RMB) You can buy ticket at Nanning train station. But that’s expensive! You should buy bus ticket from Nanning to PingXiang (66RMB ~ 10$), pass YouYiGuan, get in Vietnam (Langson) and take a small bus (5$ ~ 30RMB) that’s good idea!