Thanks to everyone for their advice and support. I know it's been ages since my original post and I'm sorry for never giving you guys an update. I was preggers at the time of my original post and had my first baby not long thereafter. I intended to let you guys know how the situtaion got resolved, but life got baby crazy and it just slipped my mind.
The MAC store that I took my niece to was not the normal store that I usually go to because my niece lives in a different city from me (about 30 or so miles away). The MAC store that I usually frequent is just fabulous, with wonderful MAs and SAs -- I really wish I could have taken my niece there to begin with!! Rather than make the drive all the way to make a scene, I actually went in to talk to the manager of the MAC store I usually go to. She was unbelieveably helpful and also quite upset by my story. She placed a call on my behalf to the other store manager to raise the issue.
The explanation that I got was that the MA that had worked with my niece was in no way trying to be rude, but was feeling "under the weather" that day. She was supposedly not being friendly and was eager to go on break because she had a bad cold. Personally, I know what I witnessed and I don't buy it. Not one bit. I made a point of stating that regardless of her explanation, I did not want this MA to get credit for the sale. The manager of my local MAC store assisted me in processing the full return and then rang me up again so that another MA in her store (one that has worked with me a lot in the past, and that I just adore) was credited for the sale. They then invited me to bring my niece in for a new appointment free of additional charge.
Since I had my baby, it was actually several months before I was able to plan a new outing with my niece and take them up on the offer. It was coincidentally around the time of the Hello Kitty release that I finally brought my neice in -- which was perfect because she loves HK!! She got a whole new makeover and detailed instructions from the MA on how best to apply concealer, and to clean her face and brushes well to prevent more breakouts. We also purchased several of the HK products.
All in all, a happy ending -- my niece was thrilled and looked just beautiful. Though now my sister is scolding me for creating such a makeup addict.
Thanks again to everyone for their support and feedback. You guys are truly wonderful. I actually thought about showing my niece your comments so she could see how outrageous the original MA's behavior was and that it was definitely not her fault. In the end, I didn't because I was afraid it would embarass her more, but I know that it would have warmed her heart to know that she had all of your support.