Somehow we owed taxes. Could someone help me double check?

I've used FreeTaxUSA for years, so I'm familiar with the process. We have a pretty simple tax situation. This year, though, we ended up owing taxes despite making less…

Our only income is from two W-2 jobs. We have a condo loan. We have a single teenage dependent. We've always filed jointly.

Line 1a:    104,828
Line 1z:    104,828
Line 9:     104,828
Line 11a:   104,828 (AGI)

Line 11b:   104,828 (AGI)
Line 12e:    37,857
Line 13b:     2,750 (add'tl deductions)
Line 14:     40,607 
Line 15:     64,221 (taxable income)
Line 16:      7,230 (tax)
Line 18:      7,230
Line 19:      2,200 (CTC)
Line 21:      2,200
Line 24:      5,030 (total tax)
Line 25d:     4,459 (tax payments)
Line 37:        571 (tax paid minus tax payments)

So the math is mathing. But what I'd love to know is why enough tax wasn't taken out.

On my W-4, I claim myself (married, joint) and our kid. I make more, so that's why we did it on mine. My wife's W-4 is just herself (married, joint).

For now, we've adjusted her W-4 to deduct an additional $50 each paycheck.

Here are our W-2s (I know that state withholdings don't matter, but I'll provide for brevity):

**Mine**

Wages:          70,424.15 
Fed tax:         4,333.00
SS wages:       70,424.15
SS tax:          4,366.30
Medicare wages: 70,424.15
Medicare tax:    1,021.15
Box 12a, DD:    10,738.87
Box 14:    WA PFML 504.23 
  WA Workers’ Comp 603.42 
             WA CF 444.49

**Hers**
Wages:          34,404.11 
Fed tax:           126.06 
SS wages:       34,404.11 
SS tax:          2,133.05 
Medicare wages: 34,404.11 
Medicare tax:      498.86 

So… It looks like the withholding is the issue. As it should be. 6% of mine comes out, while 3% of hers comes out.

I don't think mortgage matters, but here it is:

FORM 1098

Line 1:   30,017.59
Line 2:  389,054.85
Line 4:        0.00
Line 5:    2,441.04

Is the lesson to be learned here, "don't claim your actual tax situation"? Should we have her claim single on her W-4?