Can you put her in a pet carrier and bring her to a vet? If needed, a
vet can sedate her for a better look. A swollen lip can signal a lot
of things (infected tooth, kitty acne, possible sarcoma, etc. ) and at
her age, earlier treatment is better than waiting.

Look up "eosinophilic granuloma".  "The eosinophilic granuloma produces
a classical swollen lower lip or chin..." - picture here, midway down
the page (black & white kitty):
http://marvistavet.com/html/eosinophilic_granuloma.html

I have found in our cat that it responded to supplementation with the
amino acid L-Lysine.  L-Lysine counters L-Argenine (arginine).  People
with cold sores, or herpes simplex seem to benefit from controlling the
lysine/argenine balance.  Eventually he didn't need it anymore, with no
recurrences, perhaps due to a change in diet also affecting that balance.