1. Don't loose your newly-adopted child's green card. It will cause you stress.
2. If you loose it, be prepared to pay $370 to replace it. Search your entire house several times over to make sure it is actually gone. Balk at the fee (which includes $80 for biometrics... um, for your toddler...) and decide that maybe you don't actually have to replace it.
3. File for a social security number for your child as soon as you get their green card. If you need a SSN to file taxes, but have lost your child's green card, file for a temporary taxpayer ID number using the visa on their passport with the I-551 stamp.
4. Find out if you need the green card to file for readoption. You probably don't. File for readoption so that your child can become a citizen and you won't have to worry about her green card. This can probably be done without a lawyer.
5. Feel better once you realize you will, in fact, be able to file your taxes and take advantage of your adoption tax credit.