When Jan uses opportunist, she "may move 1 space"

If that space is difficult terrain which requires two movement points can she go there or is the point added to her pool or is it an interrupt of her own turn to use one movement point and then continue her move?

Rules Reference (p.19)

Move X Spaces : If an ability moves a figure a listed number of spaces, this movement ignores movement point costs. All other effects of terrain and figures apply (for example the figure cannot end its movement in another figure’s space).
When moving in this way, a large figure’s base cannot rotate and must retain its orientation.