http://bulbapedia.bulbagarden.net/wiki/Mom#Items_given_2
These items she only gets you once:
Super Potions (she ends up buying you two Super Potions, one at one time, the other at another)
Repel
Moon Stone
Silk Scarf
Hyper Potion
Choice Scarf
Focus Sash
Muscle Band
Then the Super Effective Berries she'll buy you five of at one time infinite numbers of times.