Tenant insitu whose a hoarder - evict?

Possession - Section 8 and Section 21

My tenant moved in 30 May 2019. It became immediately apparent that she is a hoarder. The 1 bed ground floor flat was cramped floor to ceiling with belongings, in every room, including the kitchen and bathroom. The front garden is totally covered in pots, old mattress, garden trellises, garden furniture etc etc.
Since then I have offered my tenant assistance on numerous occasions, I have also taken car loads of stuff to the local tip for her. I have stressed to her how this is not good for her health and there is also the potential for vermin and its a fire hazard. I inspect the property each month and each month she promises she will tidy up. She pays the rent on time each month and wants to stay long term.
I am not making any headway at all with this tenant and feel I am coming to the end of the road.
Do I evict a nice lady, who pays her rent but lives like a pig, as I am concerned for the long term potential damage to the flat and garden if I let her stay?
Can I evict her in the current climate by issuing a Section 21?
Has anyone had a similar situation whom could offer any advice?
Thank you.