Yes Ionn is right...she is number 7 in the yellow/green wave 5 bags.
All of the most recent waves have the 5 digit numbers. Although to confuse things the 5 digits seem to vary slightly sometimes - sometimes they all start with 5, sometimes with 7, sometimes with 8, etc. However you simply discard the 1st, 3rd and 5th digits and whatever the 2nd and 4th digits combine to make is the number of the pony inside. So Luna could be 50578 or 70679 or so on.