Hi Tina - are you sure you heard your teacher right?
In Rumba (I presume you mean International style) when you dance the walk, the body moves after the fooot is placed and not the other way round. There should always be a slight feeling of falling forward, with the feet moving forward to counteract this. The body then moves after the weight is taken. The knee is then locked back producing a straight leg which in turn causes the hip of the standing leg to dispace to the side and back. Tension shoul still be kept in the non-standing leg.
In order to achieve the correct poise try the following exercise.
1.Stand upright with the feet slightly apart.
2. Allow the upper body to move forward slightly in advance of the legs. But be careful not to overdo it. You should get to a point where you feel you are about to fall forward.
3. At this point move the free leg back so that it is in the correct position to start the walk. There should be tension (not too much) in this leg.
4. Swing the free leg passed the standing leg toe-ball until it is in front of the standing leg. At the full extent of the stride simply lower the heel and settle the weight into this leg, locking the knee to displace the hip.
5. The body should then move forward to attain the same position as you had at the start.
The repeat.
A couple of things you should be aware of.
1. The hips displace because of the poise and the locking of the knee. You should never force the hips - this is bad dancing.
2. The upper body can be divided into the 3 parts:
the top - which hardly moves
the chest/stomach area - which moves slightly
the pelvis area - which moves the most.
You may be making a mistake in thinking that Rumba is all about wiggling your hips and shoulders as much as you can, but this is incorrect.
If you really need to develop mobility in the top of your body then try isolation exercises - isolating the different moveable parts - shoulder - chest, hips etc.
Hope this helps
Steve