Security deposit return

[Kosh Vokter]

I have a lease coming up due and the lease agreement has 2 people (not related to one another) on the lease with an initial security deposit of $1000. The lease agreement didn't clarify how much each of them contributed towards the security deposit. Don't have the original checks from them because this is a really old lease that has been renewed multiple times and the bank info changed.  

1 of them wants to move out now and is saying she put in 1/2th of the security deposit - which makes sense. should we go with what she says, and cut a check for $500 to return her portion of the security deposit and maintain that record? I have no reason do doubt what she is claiming..