Me=W2, wife=self-employed. should the estimated tax payments made be based on her income alone or our combined adjusted gross income?

I have all my deductions done through my employer and my wife makes quarterly payments based on her income, but our concern is whether or not we've been making enough in terms of a payment. We're just not sure if the payments are supposed to be based on our gross adjusted income or just hers. For what it's worth, we're filing MFJ (married filing jointly).