Maybe it's this?
https://www.mangago.zone/read-manga/three_lifetimes/
This is a manhua about two gods that undergo a trial to achieve a higher level of godhood by living through three mortal lifetimes. The girl doesn't lose her memory (from what I skimmed) though. Otherwise the 1st life being her raising/mentoring the ML and being a boy in the 2nd life match up.
If it's not this one, I can keep looking. The trial of reincarnation screams Chinese folk religion inspired to me, so it bet it's probably a manhua and maybe a manhwa.
I LOVE YOU OMG THANK U SM Σ(っ°Д °;)っ im so dumb… the name is self explanatory ╥﹏╥ you’re amazing thank u again I really appreciate it <3
ill literally offer my first born child to you (●'◡'●)ﾉ
ive been looking for a certain thing idk if its manga/hwa/hua. but from what I remember there's this girl who's sort of like a goddess or deity of some sort and she has to experience humanity as a test of sorts. anyways she and this guy both have to go to the human world and reincarnate 3 times I forgot if they had a certain mission I think they had to find each other among all the other humans without their memories. in the first life she took care of him and was like a sort of mentor towards him? but she sacrificed herself for him and was reincarnated. then in their next life she was a guy and he was a girl and she was really popular with guys bc they found themselves being attracted to her even though she was a dude and the guy would be jealous. but HE LIKED HER IN BOTH LIVES. im like actually going crazy I cannot find it at all and ive been looking for I think 2 years now please help ╥﹏╥