Well, do what I did. Make a copy of your credit card as well. You and your wife will have different credit card numbers. On the bank statement circle the credit card used, and put a copy of your credit card with your number on it. If it makes you feel more comfortable, mark out the the numbers that are "x'd" out on your statement.

USCIS knows that married couples or couples in long-term committed relationships will have joint accounts. Same with minors and their parents. Do not worry about it too much.