Adopting my half sister from Africa

Dear memers,
The reason I brought it up here is because it is immigration related. As my sister is subject to border control.
Please I need help on how to go about adopting my half sister from Africa. We share the same dad but different mums. Our Dad passed away 8 years ago. My step mum has since taken care of her. Although things have been really rough for them since dad died, my step mum is now no where to be found. My half sister is curently living with extended family who find her a burden. She is 15. 16 in July. I am currently a British citizen with 2 kids of my own. Am i able to adopt her and bring her here to live with us?

If so what do I need to do, and how soon can she join us?
It breaks my heart to know that she might not be wanted over there when I would love to look after her and make our dad smile from above.

I look forward to your reply/ies.

Kind regards
Jazz

See also:

17. SET7.18 How do adopted children qualify for settlement?

Adopted children.

Guidance on how adopted children can become British.

Adoption: nationality policy guidance

Adoption.

Chapter 3: acquisition by birth, adoption or parental order (nationality instructions).

Complications.

Immigration and nationality law for adopted children

New intercountry adoption guidance arrives after long absence > Adopted children and children coming to the UK for adoption

The Theis case: immigration and nationality law for adopted children > US physician assistant may be forced to quit UK because of visa nightmare > Adopted sons of American NHS specialist granted visas after being denied UK entry.

FAS v Secretary of State for the Home Department & Anor [2015] EWCA Civ 951 (05 October 2015) (Must complete adoption before 18)

HU027922016 [2018] UKAITUR HU027922016 (12 April 2018) (an analysis)

New intercountry adoption guidance arrives after long absence > Adopted children and children coming to the UK for adoption