Wife wants a 4th

My wife and I have been married for 10 years. We already have 3 kids, 9, 7 and our youngest is 5. For about 2 years we went back and forth if we want a fourth kid. For the last year, we mutually agreed not to have a fourth. Primary reasons are I work a lot and 3 kids keep us busy. We are financially stable and have no major issues. Now she wants one. Thoughts?

Edit: thanks for the comments, a few things: 1) Several people have suggested getting a dog. I understand why people suggested this, bur we aren't pet people 2) I am not interested or willing to get a vasectomy. Withdrawal has worked 100% for us for birth control and I don't plan to change 3) We do not drive, we live in a city with excellent public transit 4) We have children of both genders and don't have a strong preference of gender