Although it could be an insect bite or something else rather harmless, I would quarantine her thoroughly (incl. washing hands, changing cloths, tending to her last...) right away, just in case it's contagious. I had an Myxo outbreak 10 years ago, and I'm a bit nervous since then, first things I noticed were swollen eye lids and puffed faces, had no idea what I was dealing with. But they didn't stop eating right away, instead soldiered on for about 2 weeks, so some differences there, no need for panic but caution.
Are only the lips swollen, or eye lids, base of the ears too. Ears look reddisch (I have no experience with lops though), are they hot?
No idea what insects or spiders you have around, but I would think that rather unlikely. Another thing I could imagine would be tooth issues, injury, abcess or infection in the mouth area, haven't seen that irl, but I would have a close look.
First thing I, personally, would do now, after quarantining, is giving her some pain med to see if it helps (Meloxicam (0,3mg/kg), or in a pinch Ibuprofen (ca. 4mg/kg)), offering her everything she might eat, give her water - holding the bowl to her lips or syringe feed some if she doesn't drink. When one doesn't eat I hold hay or whatever yummy fresh stuff I have (hogweed, dandelion, leaves from roses, willow or apple .....) against their mouth until they bite it out of anger, sometimes they gkeep munching on it once it's in their mouth, a good sign.
Medirabbit:
http://www.medirabbit.com/Safe_medication/Analgesics/safe_analgesics.htm
Old Thread on RCO with some suggestions what to check for, pics are gone but in that case it was an inner ear infection, a lop too:
https://www.rabbitsonline.net/threads/swollen-lip.57577/#post-792166