Wow, there is a whole lot of double-posting going on here, not to sound bossy or anything, but both of you should delete your double posts.
Anyways, to defeat the Battle Pike, you need to make it to the end of it, which means that you have to go through 14 rooms. (Actually, it is closer to being 7 rooms, because you only have an event in every other room.) After you complete the Battle Pike 2 times in a row, (Without losing to anybody inside the Battle Pike.) you will meet Lucy at the end of the Battle Pike on your 2nd time through. If you defeat her, you will earn your Silver Symbol. To get the Gold Symbol, you will need to complete the Battle Pike 10 times in a row (again, without losing to anybody in the Battle Pike.) to encounter Lucy again.
Finally, check out this sticky link for more Battle Frontier help...
http://serebiiforums.com/showthread.php?t=92364