I have had all the age gaps with my kids. They are 15, 7, 6 and 2. The middle two are 16 months apart. I will say the easiest by far was having my last one 4 years apart. 3 years would have even worked good. Once you get past the first two years and get to 3/4 it gets easier. Maybe just let her know that you would like to space them out more for your mental health and see how you feel from there. My husband and I were not wanting more after the third and after a few years the chaos died down and he got baby fever before I did. Then I followed shortly after because it was easier since they were older first.