I’m not a lawyer, so take with the obligatory grain/cube/saltlick of salt, and check w/ your attorney.
I think you can include at least part of the credit card balance as part of E/D, if you can somehow detail how much of the balance is/was separate, and how much is/was marital.
Given that you’ve had the card over 12 years, and were unmarried for a very short period of time after obtaining the card, however, any separate portion is likely to be small. And if the balance hit $0 or less during the marriage, I think that the separate portion would also be $0. (Any balance accrued since DOS would be separate, however, unless the credit card was a joint card.)
Of course, if you want to motion that it be deemed separate, I don’t think that would be an issue, although your attorney might raise their eyebrows a bit.
At the very minimum, if you’re not motioning for it to be deemed separate, you will probably need a statement (or at least a figure for the balance) as of date of marriage, date of separation, and now.