Being 5'4" is going to make getting to the ball for a smash harder, but it won't necessarily make it any harder to hit the smash if you're in position.
The reason most people stink at smashes is because they never practice it. When I was in high school, I spent a summer practicing tennis and we hit smashes almost every day. By the end of the summer my smash was a very strong shot.
The video you cite is good to learn from. Make sure to turn to the side, move to position, hold the continental grip, use your off-hand to time the ball and then turn and pronate (internally rotate) into it. The closer you are to the net, the less you need to worry about pace as the opponent(s) have very little time to respond.
Start practicing overheads every time you practice. If you can't find someone to practice with, you can hit a high ball and then get under the bounce. This can even be done against a wall. Good luck and start practicing.
