They're neither "Queens" nor "goddesses". They were all different. Maedb was a queen. Macha was a goddess. Tailté was the wife of a High King of Ireland.
The dark green with "G S" is the livery she carries now, since 1994 or so. She arrived in the north in standard CIE lined green, which she still carries, but without any markings. In her thirty-year stay in Belfast, she remained without markings. It was only once she entered the UFTM in Cultra that she acquired the "G S"; this variation of the livery was never, of course, carried in traffic - in fact she has never so much as turned a wheel carrying this lettering! So, IRM are simply giving another "fun" option in providing the model in what might be called its "Museum livery", in the same way they're offering it in the works grey it carried simply to have a photo taken when new.
With the real thing only every having two operational liveries, it's a nice - and unique - additional option.