Should i talk to my step daughter about periods, sex and boys?

Shes 10. Idk what the age is for "the talk" if shes too young idk but shes getting boobs and getting cramps onece a month without the period and we took her to the dr who said periods will be coming next......the teenagerish tantrums have started already .... uggghhhh

Ok so shes not mine biologically. Her mum is a drug addict who cbf doing anything for her and we are in the process of getting full custody of her and her brother. Been with her dad for 4 years almost we are engaged and she spends 90% of time with us.

I told her Dad about it and he suggested i do the talking cause her mother wont and he said he doesnt wanna be the one to tell her. So what do we do?