Well, I learned a little more about the whole thing today, and my Mom called the store manager...
In a chat with my Dad about the whole silly ting this afternoon, he told me that when they were told the old policy in January, it went more like this:
Mom: Excuse me, but do you have any of this style left in an XS Petite?
Salesgirl: I'm sorry, we don't. We probably won't have any more until next winter.
Mom: Oh. Well, can I still exchange this stuff then?
Salesgirl: Of course. Just make sure you bring your receipt!
Mom: Won't that be an awfully long time?
Salesgirl: No, not as long as you have your receipt.
As well, it turns out I was slightly wrong in the original post - the stuff was worth $120 regular price, about $80 when Mom bought them. Not a big deal, as the money was a small part of the issue, but in terms of the amount they offered back, I guess it does make a difference.
Also, when Mom called the store this afternoon, she asked for the manager. The woman put her on hold and talked to the women who talked to my Mom yesterday. They obviously knew they messed up - they told her they offered her $18 for the jacket and $20 for the pants! (They actually offered her $6). The manager apologized profusely for their actions, but couldn't offer Mom more than the $38.
At last check, Mom was going to fix it herself. Not that she has time to, but I'm not about to sidle up to the sewing machine any time soon! (My sewing projects always ended up looking like the "designer" shirt Denise made for Theo on The Cosby Show) She got the apology, which is what she was really after, so its OK. I told her I have the contact information for the higher ups (thanks, those of you who provided those for me!), so I'll keep you posted if any more comes of it.