To think this could be very serious?

Brilliant update. @LT2 I think people tried to share what they knew; no one should be made to feel silly over it. We can only go on what we have from the OP. The picture did look particularly bad, and even some of us who have seen a lot of shingles presentations have never seen a single lesion look quite that bad and in such a sensitive location (I was particularly worried about the sunken quality combined with the color, not just the color). However, I said the same things that I’d say again: at first, based on photo alone, I was very concerned it was cancerous. Then, based on really good points by @MissLucyEyelesbarrow , I revised and stated that if others had seen shingles presentations like this, I would absolutely admit it’s possible it’s shingles, and if the GP had a positive shingles test, then it would make much more sense for them to be so sure it’s shingles, and be treating this with antibiotics and steroids, and only refer if it didn’t respond after a week of such treatment (which it now has). But with the amount of pain OP’s mum was describing, I was still concerned that she be receiving some urgent treatment (and it sounds like she was receiving a few medications in tandem), to ensure she wouldn’t have any lasting pain in her trigeminal nerve. So glad this turned out well, and I hope your mum continues in her recovery, OP.

@5YearsLeft I was referring only to the few that said 'shingles my arse', 'that's definitely not shingles' and those saying to complain about the doctor and badmouthing the doctor. Nothing wrong with any of the posts encouraging OP to push further, which were the vast majority.