(I don't own these pictures. All Rights go to the owners.)

Name: Brianna Tennyson
Gender: Female
Age: Same age as Ben
Crush: Kevin Levin

Species: Half Human and Anodite
Friends: Ben 10 Allies
Enemies: Ben 10 Enemies

Family: Carl Tennyson and Sandra Tennyson (Parents), Ben Tennyson (Older Twin Brother), Gwen Tennyson, Ken Tennyson, Sunny, Joel Tennyson, Lucy Mann, Clyde Fife and Camille Mann (Cousins), Max Tennyson and Verdona (Grandparents), Frank Tennyson and Gordon Tennyson (Uncles), Natalie Tennyson and Betty Jean Tennyson (Aunts)
Other: Second Wielder of the Omnitrix.

Sounds like Mackenzie Foy