The teenager, who played for Devonport Services Under-18s last season and his set to feature for Plymouth Albion Ladies this coming season, came on as a replacement as England ran out 46-8 winners in Nottingham.
Tuima even managed to add a conversion on her debut and earned praise from England head coach Jo Yapp.
She was one of three players who were handed debuts from the bench in the second half, with Hollie Cunningham and Ellie Mulhearn the other two new faces in the squad.
Yapp said: “We are really pleased with the performance, the girls worked really hard to put into practice what we have been working on in this summer camp.
“It was great to see new players such as Lagi, Hollie and Ellie winning their first U20 caps.
“We now focus on the next game as we know Canada is a strong side and we are expecting them to regroup and come hard at us on Monday.”
Among England’s try scorers was former Plymouth Albion player Lottie Holland.