She is probably hungry...there is a chart (hopefully someone will re-post) to show you what the prey should weigh for a given size snake, or you can compare
the prey to the snake's (un-fed) body: the prey should be roughly the same diameter (not larger than) the mid-body of the snake. She is likely ready for medium.
Always feed IN the snake's normal enclosure...there is no truth to that bit about avoiding aggression this way, if anything, it makes it worse since you are trying
to handle a snake that is hungry, and then trying to put the snake back that is still pumped up (in "feed mode") & is very likely to bite you.
Few snakes are actually aggressive, most bites are defensive (out of instinctive fear) or confusion about food...most bites are avoidable. Another thing that makes
snakes MORE likely to bite is feeding live prey. Not only is it unsafe (sooner or later your snake will need the vet...rats bite hard, & can actually kill the snake, either
directly or by injury & infection that doesn't respond to treatment) but it keeps your snake in a highly-defensive snake, never knowing when a live rat shows up
that she must do battle with. Snakes fed pre-killed (f/t OR fresh killed by you) tend to be calmer pets, though it may take some time for yours to learn to relax now
that she's used to live.
Bad idea feeding another rodent only a few days after the first...likely to cause a regurgitation of both. Snakes need time to fully digest & replenish digestive enzymes.