Have you spoken to the tenant @saraclara ?
I'm wondering if she wants to be evicted, in the possibly mistaken belief she'll get council housing? Those days are gone in many parts of the UK. Even if she does eventually get it, she's facing a long time in substandard temporary accommodation first. And if she doesn't have children she's got no chance.
She could simply be a bad tenant. I'm sorry if that's the case. Your options then are to either evict (Section 8 or section 21) or sell below market value. There are landlords who will buy any property regardless of state of the place or type of tenant. Often cash buyer investors.
However another possibility is she's not intentionally defaulting on the rent. She might literally not have the money.
The disastrous consequences of the removal of housing benefit. The insufficient replacement rarely meets market rent in many areas. Terrible for tenants, terrible for landlords - and terrible cost to society (and I don't just mean the billions spent on substandard temporary accommodation).
Obviously it's not your fault various governments have failed to provide sufficient benefits safety net and affordable (social rented) housing.
To deal with your specific situation - if the problem isn't deliberate non payment, you could discuss a rent reduction with your tenant? Or if she's on benefits and is defaulting on rent, you can request direct payment of her housing benefit to you.
Really the problem is the need for more social housing. Private renting works when it's someone young and transient and relatively affluent. Or needing somewhere short-term (in-between house sales, working away, trying out a new area if relocating). It's not in any way an appropriate alternative to social housing for older people, settled in the community families, and those on low incomes (disabled, low wages, or carers).
The only alternative to more social housing is increased housing benefit. The former is cheaper and better for individuals and for society.