As many as she wants.
diagonals
The three major diagonals in an ordinary hexagon do not intersect at the same point. Therefore, in such a hexagon, the diagonals form 111 triangles.
a cornere
Select any one of the vertices and draw all the diagonals from that vertex. This will divide the polygon (with n sides) into n-2 triangles. Use the coordinates of the vertices of each triangle to calculate its area, and then add the areas of these triangles together.
A regular hexagon can be divided into 6 equilateral triangles by drawing diagonals between opposite vertices, if that helps.
They are diagonals. In a rhombus, diagonals join opposite vertices.
diagonal
There are 21 vertices in seven triangles.
Opposite angles
3 squares and 4 triangles will have 24 vertices. There will be 4 vertices for each of the 3 squares. Since there are 3 squares, that will be 12 vertices. There are 3 vertices for each of the 4 triangles. Since there are 4 triangles, that will be 12 vertices. 12+12=24.
Only a square and a rhombus will have all its diagonals bisecting vertices. In other shapes some - but not all - diagonals can bisect vertices.
They are straight joining vertices to non-adjacent vertices.