Patricia Alejandra Lorenzo Harris travelled from Rawson to Blaenau Ffestiniog, Gwynedd. a year after the towns were twinned to mark 150 years since the migration.
She said it was a "dream" to visit her great-grandfather's home country.
Next year a grant will allow someone from the town to visit Rawson.
The first Welsh settlers to reach Patagonia founded Rawson, which is the capital of the Province of Chubut.
Among the nearly 200 settlers who sailed south on the Mimosa in 1865, at least five were from Blaenau Ffestiniog, and the towns were twinned last year to help re-establish the link.
Historian Ms Harris, president of the twinning commission, travelled with her friend Marisa Conde to learn more about where her ancestors came from.
They visited the Welsh Highland Railway, Llechwedd Slate Caverns, took part in a Spanish lesson at Aberystwyth University and visited Ysgol Maenofferen where they presented gifts from children of 178 Suyay Hue School in Rawson.
Ms Harris said: "It's been my dream to come to Wales and see the country. When I was young, I spent a lot of time speaking to my grandfather and he told me about how his father had travelled from Wales with his family.
"I also feel a great responsibility to bring greetings from the whole of the community in Rawson and to re-establish the link between between Rawson and Ffestiniog."
A descendant of two of the first people from Wales to resettle in Argentina's Patagonia has visited the north Wales town where her relatives came from.