Swollen and pink bottom lip - welcome any advice!

Saturday 19th Nov noticed the bottom lip of our dog looked slightly swollen. Got worse so took the vet who prescribed  Vetasepta and gave steroid injection. Applied twice daily. Back to vets today as no progress, maybe little worse, who gave another injection and gave antibiotic tablets. Vets say could be reaction to something which she came in contact with but I think it would’ve gone down by now. Wife thinks small cut in mouth which has become infected but I can see anything when I check. Will note she doesn’t seem to not be herself. Eats and drinks we’ll, still wants to play and go for walks. Below image shows best comparison. Left is how it looks now, right is from few months back. Lip was thin and black. Now swollen and pink. Anyone have any experience or knowledge around this? Thanks

Hi - frequently, a steroid injection given for swelling works impressively fast.  If it doesn't work twice and antibiotics don't do the trick, I wonder whether the swelling might not be inflammation, or not be being delivered to the site for some reason.  Your vet might ask to biopsy.