I read your profile and noticed other pets - any other kitties they could have "snagged" her by chance on the lip? and how old is Jill? Once of my cats had a swollen lip once as well ... even though I keep mine inside, but they do have an outdoor custom built "palace" (cage) for the day, it was a flea bite that caused it. I keep them on frontline but only during the summer months - and down here in VA that means starting in March through October!
This may be a suggestion for you ... or please check out teeth and gums ... is why I asked for her age ... they are like us and tartar/plaque build up does occur and can cause this type of swelling along with a bad tooth in that area. Any signs of pigmentation change at this swollen site to must be checked for, could - but not usually cancer. I will check a site that I have for further information on this to see if we cannot get some more answers for you ... I/we understand the financial situation that can happen to any of us at any time.
I'll post back shortly.
"There are two means of refuge from the miseries of life: music and cats." - Albert Schweitzer
If you know my location, then YOU are IN TUNE...