Tenants not leaving even after section 21 has been issued?

The chances of her being rehoused are slim to none. Then Council do not have any interest in rehousing her.

You should look to enforce the s21 and I suggest you get good legal advice without delay. I am afriad that nobody else is going to help you in this situation.

I hope for your sake that you deal with all the pre-start compliance requirements. If not, then you cannot rely on the s21 and you are stuck with the tenant, although you could pursue for rent arears.

In this situation, your tenant is unlikely to move out until you obtain a Court order for possession (and there is no way you can force them to move other than by instructing bailiffs for which you need a possession order).
You should move to start proceedings asap as the courts are very slow, and it could take up to a year or more.
If you are unfamiliar with this work, you should use solicitors - Landlord Action are a good option. My Landlord Law service has a step-by-step guide for members for those who are willing to give it a go acting in person. https://landlordlaw.co.uk/what-is-your-problem/. We have a free preliminary guide at https://landlordlaw.co.uk/openaccess_trails/which-possession-proceedings..
If you are desperate to sell, you may be able to sell the property with her as a sitting tenant. There are companies who specialise in this but you may not be able to achieve the full market value.

"If you’ve got evidence of a mandatory ground like rent arrears use only that ground. Mandatory means that the judge must grant you possession, don’t give the tenant anything to fight."

https://www.landlordvision.co.uk/blog/recent-eviction-cases/

Evicting a Tenant on Relevant Grounds

The tenant was in serious rent arrears, well in excess of 8 weeks (rent is paid weekly) but the landlord waited until after Christmas and had hoped to use Section 21. Unfortunately, he had missed the last Gas Safety Inspection by a month and therefore could not meet the requirements of question 17b on the N5B (see above).

Left with no other option the landlord served a section 8 on ground 8 (a mandatory ground). I have no idea why landlords believe that section 21 with 2 months notice before action is better than section 8 with 2 weeks notice before action when they have mandatory grounds, nor why they allow the arrears to climb into thousands of pounds before going for possession, this is the case here.

I had told the landlord to stick to a simple mandatory ground 8 because the rent arrears were so high that the tenant would need to win the lottery to pay before they got to court. Unfortunately, the landlord decided to add the Anti-social behaviour discretionary ground to improve his case, which was valid but guaranteed that the tenant would defend himself. He did, and the judge told him to pay his rent in full the following day and £20 extra towards the arrears and scheduled a second hearing to hear the tenant’s defence. Despite there being a mandatory ground, the court-appointed solicitor managed to distract the judge because of the accusations of anti-social behaviour. There will now be another hearing AND the tenant hasn’t paid another penny in rent since, 5 weeks more so far.

Get real. Serve a fast track Sec 21 straight away, you are never going to get your money back and the council will never rehouse a tenant who is in rent arrears. Sell the house PRS is not for you.

The first thing tenants are told is not to move out, and make life hell for the landlord financially and emotionally. The landlord is walking on eggshells all through the process up to bailiffs at the end

Its hell on earth with a Sec 21 imagine what it will be like without one.
Run for the hills Sell Sell Sell

I am a landlord that has had section 21 agreed to by the courts in April this year since 27th May 2022. When the bailiffs issued his notice the tenant decided to counter claim against me on alleged offences of which I have al the evidence to challenge. But the case was postponedon16th April 2023. When I asked the judge what relevancy the counterclaim has re the eviction he replied. As a counter-claim we cannot allow the bailiffs in and we needed the bailiffs to go in for council to rehouse. I then said the tenant was in arrears so he wouldn't be helped by the local Borough. He then told tenant he needed to pay rent. The counterclaim case must be paid by tenant and I could have my costs reassessed. This would be heard on the 1st available date after the 15th June 2023. The next case date was 4th July 2023. On 3rd July I recieved an email stating due to the lack of judicial available the case has to be postponed. Now we are in position of waiting for new date the tenant is over 3500 in arrears and he he has never applied to be rehoused. The state is unbelievable. I also have evidence that the tenant has done this before. It is mockery and it is about that when the person is not honest criminal proceeding should be appropriate.

Reply to the comment left by Clacton at 15/08/2023 - 22:25
According to the Government, lefty looney Shelter and Generation rent tenants are the salt of the earth. PRS is stuffed sell up when you can, whilst you can.
Everyone else is there must be a reazon for that

You will need to get a court order then call in the balifts to remove her if she doesn't go after the court order. The Council will wash their hands of housing her for as long as you keep her in the property. They always tell the tenant to stay put till they are pushed out.

Reply to the comment left by JaSam at 15/08/2023 - 10:57
Please be careful with S8
I have done this for rent arrears , plus the tenant refused a rent increase and a counter claim for disrepair was submitted.
Tenant has legal aid - I do not.
My case is now going to trial.
20 k in debt ( loans to pay solicitor)and I now have to sell the home I live in to pay off the loans .
No guarantee the tenant will have to leave , depends what the judge says - but regardless, I will have to leave my house.
Just be sure you have all your paperwork in place if you do go to S8 and please check the property and be positive there are no outstanding repairs