Hypothetically speaking, yes. But she'd struggle to sell it with a tenant in situ, and current laws prevent her starting legal proceeding to evict the tenant.
As i said above, i've not got any sympathy for her, but unfortunately it's not easy for her to get out of her situation.
Who cares about her struggles to sell? She can reduce the price until she can sell. Or the foreclosure process will do that for her. She made the wrong investment and does not deserve to be bailed out, nor does she deserve any sympathy. Her entitlement that she believes she deserves to get universal credit when she's a BTL landlord is absurd.