She says the burning pain is unbearable. ER wait is 8 hours! What can we do?

The rash in the photo looks highly suggestive of shingles (herpes zoster): clustered fluid-filled blisters on a red band of skin, apparently limited to one side of the torso. A photo cannot confirm the diagnosis, but the description of unbearable burning pain fits shingles very well.
I would not simply wait 8 hours without trying to get medical advice sooner. Shingles is best evaluated promptly because antiviral treatment works best when started early, particularly within about 72 hours of the rash appearing. Severe pain itself is also a reason for urgent assessment.
While waiting to be seen:
Call an urgent-care service, doctor, or pharmacist now and explain that she has a new blistering rash with severe burning pain and ask whether she can be assessed sooner than the ER.
Keep the rash clean and dry.
Apply a cool, clean, damp compress for short periods to help with the burning.
Wear loose, soft clothing so it doesn’t rub against the blisters.
Don’t pop, scratch, or puncture the blisters.
If she normally can take paracetamol/acetaminophen safely, it can be used according to the package directions. Don’t exceed the recommended dose.
Don’t start leftover antibiotics, steroid medication, or someone else’s prescription medication.
If she takes blood thinners, has kidney disease, stomach ulcers, liver disease, or takes multiple medications, ask a pharmacist or doctor before giving additional pain medicines, particularly anti-inflammatory medicines such as ibuprofen.
Until the blisters crust over, avoid direct contact between the rash and anyone who is pregnant, severely immunocompromised, or who has never had chickenpox or the chickenpox vaccine. Someone exposed to the fluid from shingles blisters can develop chickenpox rather than shingles.
Go for emergency assessment rather than waiting if the rash is on the face, around the eye or nose, she develops eye pain or vision changes, becomes confused or very weak, has severe headache or neck stiffness, difficulty breathing, widespread blistering, or rapidly worsening illness. Shingles involving the eye can threaten vision and requires urgent treatment.
If you tell me her age, when the rash first appeared (hours/days), whether it is only on one side, and whether she has fever or any rash near the eye/face, I can tell you how urgent this situation appears and what to do while waiting.