This is my mother in law. She never really tries to buy anyone personal gift (my boys are 15 and 17 and they still get pajamas from the child section at Target). Every Christmas she gets me either gloves or slippers, sometimes both. For 17 years now I've tried to politely say they are the wrong size, but she never learns or cares.
One year my step daughter asked her for a pair of cowboy boots. She was 16 or 17, so she was hoping for a regular looking brown pair of boots, size 9. Well, she got a pair of pink and purple fake leather, probably from Target or Walmart kids section, size 5.
It wouldn't be a big deal if she was just going out and buying presents, who cares. But, she takes the time to ask people what they want and we give sizes. yet, she just grabs whatever the closest thing is she can find while looking for all of 2 minutes (seemingly) and spends what must be over $1000 on crap that either gets returned/exchanged or donated when we can't find the receipts. She doesn't give us the receipts, she will look through their house before we leave for them and sneak them out. One year her mom found her doing this and gave her a snarky "oh I see you are returning everything' comment when we were leaving. Yeah, its either return everything or donate it. How would you prefer us to not waste your money by just letting it clutter up our house unused?