April didn’t realize she was pregnant until after Jackson had already started divorce proceedings.
When April fell in love with her ex-fiancé, Matthew, again and eventually married him, she didn’t wander off to parts unknown.
She stayed in Seattle so that she and Jackson could continue to give Harriet as stable of a life as they could.
Once they worked through the tension caused by her not informing him when she found out (Arizona took it upon herself to do that), they realized that finding a way to become friends again so that they could co-parent their child with as little strife as possible was the best way to do things.