Gina wants to use models to better understand how the types of bonds in a molecule relate to the presence of geometric isomers.

which model would be most in her research?
the space-filling model
the structural formula
the molecular formula
the ball-and-stick model

Answer is: the ball-and-stick model.

Ball and stick model gives informations about bond lenght and space filling model gives information about space occupied by atoms.  

In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them.

The atoms are represented by spheres, connected by rods which represent the bonds. Every ball represent one atom in one molecule and they have different colors for different atoms (for example, carbon is black, hydrogen is white, nitrogen is blue).  

it was spontaneous.

"ain't i a woman? " is the name given to a speech, delivered extemporaneously, by sojourner truth, (1797–1883), born into slavery in new york state.sojourner truth' delivered her famous speech "ain't i a woman? " (which did not have a title at that moment) was given without any previous preparation. her dissertation took place at the women's convention in akron, ohio, in 1851.