Why does she want you to change it?
Some folks change out their sand when the bed gets old or is clearly filled with detritus, or they don't like the color.
If you do choose to change it, you want to rinse the heck out of the new sand - with either discarded tank water or rodi water otherwise you will be 'filling' the new sand with the crap in your tap water (read phosphates...).
It is also suggested that a sandbed change be done in increments (like a grid)..10% or so at a time until it is entirely replaced. In this way you do not get any spikes in ammonia as the new sand has a chance to catch up before you change the next section. Hope that makes sense!