Can I return an brush to M.A.C. without a receipt?

So my wonderful mother went to M.A.C. and I asked her to pick up the 188 Stippling Brush for me as I included it as my allowance for the month. I have not used the brush, but it is still in the little plastic bag thing it came in with the bar-code sticker still on and everything but she threw the receipt away! She bought it about two days ago and I have yet to use to or mess up the bristles or anything. Could I return/exchange the brush even though I don't have a receipt? The girls at my local MAC store are like close friends to me, but I just wanted to know if this exchange would be a problem. Thank you!