You should negotiate. If you have a lease then you may be eligible for a discretionary grant. If you don’t have a lease it’s hard to see how your landlord can enforce back rent. She can of course kick you out if you don’t pay up.
Whilst the business was closed the salon will still have had overheads but they will have reduced. Ask to see evidence of the overheads included in your rent. Waste collection, premises public liability insurance, utility bills, rates, rent, cleaning services.
Then use the argument that works for you. Offer to pay a fraction of the fixed costs of the business based on the percentage of the premises that you occupy. Or Suggest you discount your rent by the same percentage as her overheads have reduced. Be very matter of fact. No-one’s had any income during the pandemic, but bills are bills. Suggest you cover your share of her bills but not her lost income.