Doesn't anything she wears or touches go invisible too? I honestly don't know if that was this invisible girl or one of the other non-Fantastic Four invisible girl characters that exist.
I believe she not only usually makes everything she has invisible but has made other people and objects invisible. She can project it out like her forcefields. I supposed she might have forgotten it was there and not having put thought to it it might have stayed visible but its a stretch. In addition though the uniforms are made from reeds unstable molecules which react to superpowers and is why his clothes stretch and johnys clothes don't burn away and since its branded I would assume it would be made the same.
As the Invisible Woman, Susan can render herself wholly or partially invisible at will by bending light around her.[50] She can also render other people or objects fully or partially invisible too, affecting up to 40,000 cubic feet (1,100 m³) of volume.
EDIT:
Invisible Girl
Initially, her powers are limited to making herself invisible. However, before long Sue discovers she can make other things invisible as well as create force fields of invisible energy.
Or maybe it's order, obviously the mental concept of superpowers is never really explained, but hypothetically clothes etc... that are being worn are generally automatically assumed, as if it was a concious effort of "remember my shirt, shoes, bra, earing, left sock, right sock". every time would lead one to expect mistakes on the regular.
Logically what would make more sense, would be maybe if she turns invisible, then picks something up or puts something on (or in). It would most likely not become invisible.
That would be equal parts fascinating and disgusting to watch it go from whole apple, to chewed bits, to sliding downwards, to becoming fecies over the coarse of a few hours.
I mean, you knew the apple eventually becomes poop, but you never thought about the process. There must be a brief moment where its as close to being apple, as it is to being poop. Even if just for a second as it spills into poop territory.
And then she could get into wonder womans invisable plane, and use the bathroom, and poop it out.