Pale gums, parts that should be pink (depending on the rabbit color) will look white, cold extremities, lethargy, rapid breathing even at rest.
If your rabbit is happily eating, she will likely be fine. You can put a small spoonful of blackstrap molasses in her water, you can even add a small iron washer to the water bottle, and offer dark leafy greens, like blackberry leaves, kale, parsley in addition to her regular food. If she does not like the water additions do not continue--drinking enough is more important than having the iron. Offer one bottle with molasses, one plain. There are also mineral salt licks that have iron in them--the brown ones. They will be at feed stores and big box pet stores.
You can also do nothing, if she is eating, she will recover now that the fleas are gone.
