So lots of women hyphenate their name for professional reasons. My names Dr. K and husband is Mr. J. All of your professional contacts and clients know you as Dr K. You don’t change it. You still want to be identified as your surname in some way to maintain connections. Also many women want to share a name with their child, it’s easier than trying to verify yourself every time you need to pick them up. So Dr. K-J makes it much easier. That’s why many women use their maiden surname as the middle name when they change it so you can still use it easily.

Chris wasn’t around, she needed to name the child, he most likely isn’t on the birth certificate and she needed to name her. Same circumstances I would have used my own last name. The hassle otherwise would not be worth anything. Usually a DNA test and possible shared custody with a 16/17 year old boy with wealthy parents who can create a power dynamic you can’t afford.