Aaand, that sometime happen in real life too when their child already into marriagable age (idk why this kind of people usually pop up during this time), suddenly show up and shamelessly reclaim their seat in their child life. As if all this time this kind of parent(s) never abandon them.
Sometime the most shameless one even asking for their child's spouse to send them money regularly because they're THE blood related in-law/the biological parent(s).

just abandoned her kid when it's convenient for her, meet her kid again because she felt guilty and it's convenient for her to go and 'apologize' personally, and then wait for her son to forgive her while living a rich and laid-back life as it's convenient for her to receive anything her in-law gave her since she's too old to work or be back to her life before hyesung's reveal happened