Kikklik,
There are many Vietnamese TV stations on the Galaxy 19 satellite, all free of subscription fees. Lucky for you, it's pretty much the easiest to receive.
You'll need a dish, an LNB (the thing on the end of the dish that receives the signal), cable and a receiver.
All the Vietnamese stations are broadcast in standard definition, so an older receiver will be fine if you can find one cheap (are you in the Bay Area? If so, I can probably give you one). If you're going to buy one, go for an HD receiver as a station may switch in the future.
If you want a package, here's one:
https://www.satelliteav.com/shop/?ws_pid=1713&ws_cat=413
It comes programmed for the Glorystar Christian TV service, which is on the same satellite. Luckily, it's easy to reprogram for Vietnamese channels. Satellite AV can probably send it to you already set up for the Vietnamese channels. If not, we can teach you. It's very easy and a skill you will want as the TV stations sometimes move around on the satellite.
Or, here's the dish and LNB only:
https://www.satelliteav.com/shop/?ws_pid=1719&ws_cat=413
Before you spend your money, make sure you mum's place is somewhere that Galaxy 19 is visible. Buildings and trees block satellite signals. To check this, go to
http://www.dishpointer.com/ and put in her address and choose Galaxy 19. Move the pointer to where you will install the dish and the green line will show the direction of the satellite. The box underneath shows the angle you'll need to look up to see it. It's pretty high up in the sky, so you should be OK. You'll only have problems if there are very large obstacles nearby.