The Fantastic Four is made up of powerhouses, all of which have an argument to place them at the top of the list as the strongest member of the team. The Thing, with his brute strength is able to go toe to toe with the Hulk and come out victorious. Mr. Fantastic is arguably one of the smartest people that ever lived, even if his personality leaves... something to be desired. The Human Torch can go nova, able to burn as hot as an exploding star. The team member who arguably draws the least support is the Invisible Woman -- until now.
Susan Storm's powers began with the ability to turn herself invisible. However through pushing herself to control her powers further she discovered her abilities to create force fields. As her powers continued to grow, she discovered her ability to turn objects invisible and later outgrew her restrictions on how many things she can make invisible at once. The power of her force fields grew as well, able to withstand hits from from some of the universe's strongest hitters.
Eventually Sue's powers would grow offensive, allowing her to send waves with her force fields, to knock her foes back. Then her power set grew, allowing her to focus her force fields into knives that she could throw. Her powers of invisibility allow her to use different waves of light, giving her X-Ray vision. More recently her powers have grown to include the ability to disguise herself by adjusting the light that reflects off of her, enabling her to appear different to others.
In the preview for Empyre #1, we find the Fantastic Four on a family outing in space, when they run into the heavily armed war fleet of the newly formed Kree/Skrull alliance. The war fleet is headed towards Earth, and no one knows why. Determined to find out what has united the Kree and the Skrulls after such long conflict, the team goes on a recognizance mission. While the rest of the team laments at how weird it is to turn invisible, Sue turns the entire spaceship they are travelling in invisible.
Not only do they become invisible to the naked eye, but Susan's powers also make them invisible to radar. Mr. Fantastic comments on how she makes it seem effortless. Reed admits that Susan Richards, the Invisible Woman, it the strongest one of them all. Arrogant as he may be, Mr. Fantastic admitting Sue is the strongest shows just how powerful she is. And with Reed being one of the smartest people there are, you know he has weighed the options. As for why the war fleet is headed for Earth, we will have to wait and see when Empyre #1 hits store shelves April 15th, 2020.
Source: Marvel