The lump should be visible for a day or two...after that...it should not look like so much of a lump but a thickness of the snake's body. If the lump still looks like a lump after a few days...your temps may not be high enough for good digestion...or too hot that the snake does not like it.
If the rat was only slightly bigger than the snake's body...the lump should not be all that noticeable very long...depending on how the snake looked before. That is a good size to feed...good luck with her