Does she get reborn as a baby or is she just transferring bodies at random ages when reincarnating?

When she says she gets reborn is, is she starting over as a baby? Im just confused because when she was Ji Won, her mom said she "changed over night", assuming its the 12 year old Ji-Won she's referring to. 

So if thats the case then, does the spirit just randomly possess peoples bodies?

What happens to the original Ji-Won before the reincarnation happens, Does the previous soul just disappear or get kicked out or something? 

If she reincarnated into 12 year old Ji-Won then what happens to the hosts memories, does the reincarnation lady just inherit the hosts memories and it gets mixed with her own? 

Its hard to believe that she would start crying over her mom when she only inherited the 12 year old body for a couple months, it would make more sense if when she reincarnates she starts out as a baby, the love from child to mother would be more believable if thaf makes sense. 

The only thing I can think of that might be a bit of a stretch is she retains the orignal hosts feelings and memories and those emotions get mixed in with hers.

 My head hurts, is it useless thinking of the shows logic and just enjoy the show? Oof

 sephsmoonlight:

It's quite simple, she is reborn as a baby but she only gets her memories back from the past lives between the ages of 9 and 12, it's still her soul into any body, there's just this moment of "awakening" that happens, it's not a possession. Hope it was helpful :)

Oh ok!!! So when she awakens  its like when all her memories come back. In the recent episode she seemed to get her memories back at a earlier age? So is it random ages

Lol everything you just said makes me wonder how this got this confusing for you because it's literally an important dialogue she had already explained, but allow me. 

She never said she possesses other's people's body or reincarnate in a child's body randomly. The show is talking about remembering "past her lives" She specifically said she regains her memories from an age range 9-12, don't you remember? The "original host" you're speaking of is none than her own self. That's her body, soul, and mind, it's her life not another. She lived 19 lives of her own, she just remembers everything. So she starts out living life as a normal kid without knowing her past life, and after all those 10+ years of living memories go into her mind, it's probably hard to process them every time, hence her sudden change and intelligence at a young age.  She started crying towards her 18th life's mother because she regained her memories during that time, which is why she was doing a handstand, to relieve the headache from nearly 20 years worth of memories image how painful that is to go through physically and mentally, especially as a child to. She simply was afraid to lose another one of her mothers again in fear of dying and having to live on life losing another one of her loved ones all because she remembers them in her past life before she died hence the flashback to one of her past life years to explain why she is crying during that moments with her 18th's life's mother lmfao. 

Let me know if you need more clarity, if the kdrama isn't doing too well with elaboration you can also read the webtoon as well when waiting for each episode to come out.