A spouse is Never a dependent. You file your tax return as Married Filing Jointly even if one spouse has little or no income. The income from both of you is entered on your joint tax return. Filing a joint tax return gives you the highest standard deduction, $24,400 if both are under age 65.
You never claim a spouse as your dependent. You file a joint return.
Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $24,400 (+$1300 for each spouse 65 or older) You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit.
And you are correct--if she only worked for a few weeks the child care credit would not work out for you,