Williams set a new UK junior 100m record on Friday
Britain won gold after beating Poland by a mere 0.06 seconds to clinch the women's 4x400m relay in the European Junior Championships in Estonia.
Anchor Kirsten McAslan outpaced the pack to secure gold with Katie Kirk, Lucy James and Amelia Clifford.
Earlier, Hertfordshire schoolgirl Jodie Williams just missed a hat-trick of golds after taking relay bronze.
The 17-year-old was chasing a third gold medal in the 4x100m sprint relay after winning in both 200m and 100m.
But despite pulling back three places in the anchor leg, the world junior champion had to make do with bronze.
Germany took gold in 43.42 seconds, beating a 23-year-old European Junior record, with Italy in second (44.52) and Britain third (45.00).
The men's 4x100m sprint team, meanwhile, were narrowly beaten by France who finished in a time of 39.35 seconds to Britain's 39.48. Poland were third in 40.42.
The GB team ended the championships with 15 medals, six gold, five silver and four bronze, to finish third on the medal table behind Russia and Germany.