Child of Non EU Family Member, SS rule

[WalexK]

Hello, I urgently need advice about my wife daughter. I British Citizen, returned back to the UK with my spouse a Non EU with Family Permit, previously worked in another EU country.
My wife daughter now 15years old need to join us now from Tanzania. Please, what is the maximum age require by law for her to join us here in UK. I am contemplating there is difference requirement in Age for British Immigration Law and EU Law.
Presently my wife has 5years resident Permit of a family member of an EU (British Citizen).
We want her(daughter) to finish secondary school Examination before joining us here in the UK, this may probably be towards her 16th birthday.
Also, what requirement do we need to present at the Embassy for her to apply for a visa.
Finally, what type of visa will we need to apply for her.

I will really appreciate responds from members and non members.

Thanks you all.