There looks to be only two cast members on that movie, I'm not sure if such small casts are divided that way. But you can try to update the cast using the Edit page button at the bottom and choose "Correct/Delete" in the cast drop down box, and click Continue. If the cast members have a number assigned in the Order column, try to remove it from the cast member with the minor role. If not, try to add a number for the one with the large part (Order #1), and leave the other one without a number. If it's possible to divide such small casts, that should do the trick.
If she is credited on screen, then she should have an Order Number. IMDb does not distinguish between major and minor roles, and every person listed in the on-screen credits is treated alike.Also, Order Numbers must be assigned sequentially, so if she is third person listed in the on-screen credits she needs to have the Order Number 3 assigned.
If, on the other hand, she is not listed on screen, she needs to have the (uncredited) attribute included in the IMDb listing, and is not permitted an Order Number.