Uh-oh.......I need advice ASAP!

[SATX*APhi]

Okay, so I bought some awesome 7th row tickets to see Shakira (again). I e-mailed a friend of mine (friend #1)and asked if she wanted to go. She didn't respond after a couple of days so I asked a girl I work with (friend #2) if she wanted to go. Girl from work said yes even though she really isn't into Shakira. Okay, so friend #1 just IM'd me and said she is super excited and can't wait to go. Friend #1 (as well as myself) loves Shakira's music and has been listening to her since before she was the Shakira most of you have come to recognize today. Half of the concert is in spanish and friend #2 doesn't speak any Spanish. Friend #2 did, however, tell me yes first. I think that I will have a better time with friend #1 and I think she will have a better time than friend #2. What do I do? As of now, both girls think they are going and I only have one extra ticket. The concert is in two weeks and I need to tell one of these girls by tomorrow that they can't go, and I have no idea how I am going to do that! Somebody, pleeeeease help get me out of this sticky situation!