Occasionally, your mother will dip into your own savings and purchase you an item. Unlike in Gold, Silver & Crystal, the items you get are all standard items and most are actually useful. Unfortunately, room decoration is not in this game. She will call you up whenever she makes a purchase so you know to go and collect the items.
To collect the items she purchases, just go to any PokéMart and meet up with the delivery man in red. He will give you these items. He can only handle five items at any one time so once he reaches five items, if you have not collected them, then your mother will stop spending your money.-Serbeii
So, yes *, she does spend your savings*
Source: Above Link
Hope I Helped!!