Don't worry that you're not seeing them, your rabbit should consume them directly from her anus. (gross to think about, but we're humans so we don't really get it)
Sometimes if something is off in their diet or after a sudden diet change, your rabbit will produce more than they need to eat and you might start seeing them in her cage. Obese rabbits or rabbits with medical conditions that prevent them from reaching their butts also might not eat theirs. They have a much stronger smell than normal fecal pellets and a distinctive appearance, kind of like a blackberry. I've never seen a rabbit eat a cecal off of a surface so she probably wouldn't eat one you offered her, but every bunny is different.