Irish Child, Nigerian Mother. Can they move to the UK?

[Kaysie]

Hi all,

I don't know if this possible but I thought to ask.
My aunt is a single mother from Nigeria. She had her 14-year-old daughter in Irish.
The niece is Irish and has an Irish passport.
My aunt has another child. He's American. They all live in Nigeria.

Question is now that, can my aunt move to UK with her Children under the EU directive?
I'm aware the UK will leave the EU March 2019 and EU citizens and their dependants will settle eventually.

How will she go about it, please?