Could you lose custody of your child if you allow someone else to spank them?

Just had an interesting conversation with someone. So most parents would be irate if they found out someone physically disciplined their kids, understandably so. But this one woman told me that if someone came to her saying she/he had to spank her child, she wouldn’t initially get angry. She’d first wonder what her child did that was so severe and ask so. Then approach her child and talk to them about what happened. If she felt it was uncalled for than she’d inform the spanker that it wasn’t her go to discipline and to not do it again. 

She assured she she wouldn’t let just anyone spank her child. It would depend on who it was and why they’ve done it on how she’d react. Immediate family was different from a friend or babysitter was what she told me. 

What are your thoughts? Could she lose custody or could CPS look into this at least? The