I could see a shower for the SECOND baby of the same mother under a few circumstances (if she didn't have a shower for the first baby, then a first shower for the second baby is up to the "local rules" - might be okay, might not):
#1 - this time around it is a multiple birth (twins, triplets, etc.) - just because you had a baby previously doesn't mean that you have the equipment duplicated enough times for a multiple birth. But it isn't required - it's still up to your friends or family members to throw this for you and NO HINTING allowed - although dramatically announcing how many babies are coming is probably going to be okay, twins, triplets, and the like are surrounded by a bit of drama, naturally!
#2 - everything was lost in a natural disaster (fire or flood comes to mind, so there is nothing in the parents' possession to welcome the new little one home to. Especially if they are still dislocated from their home...it could be a reminder that "life goes on" and "life will get back to a new normal, even if not to the old normal").
#3 - it is the first baby of the OTHER parent and both parents are GOH, not just the mother.