Rick Ross' new two-month-old daughter subtlely made her IG debut this week -- only to have the spot blown up by the rap kingpin's new GF ... who might have overstepped her boundaries a bit.

Model Cierra Nichole made a post introducing their daughter Au’mei Moon Roberts ... with Rozay sharing in the congratulations for the bundle of joy by liking the news on Hollywood Unlocked.

All appeared to be well until Cristina Mackey -- Rozay's current gf -- reposted the pic, gushing over how beautiful the baby was.

Cierra didn't approve and let Cristina have it ... "stranger danger" never sounds good when it's hurled in your direction! BTW, Cristina seems to have gotten the message loud and clear, 'cause she deleted the baby post.

Now, Cristina's been spotted on RR's arm for weeks, and has quickly grown familiar to fans ... for rubbing them the wrong way with frequent posts of her lavish lifestyle, and she's even discussed their relationship in interviews.