s21 & s8 at same time?!

Possession - Section 8 and Section 21

Afternoon all,
Update: Tenant i have is starting to seriously take the p*ss! Problem is i dont think she knows it with here requests.
We agreed to increase in rent if i skimmed lounge wall and bedroom and new bathroom suite (shower etc) and i'd give her a months free rent for her to purchase new flooring in these rooms etc back in December. Feb should have been new rent....Nope just the original was paid. I contacted her ... her response was: waiting for tax credit start date and that she has been busy. Also turns out that in these 3 months no flooring has gone in. New bathroom has no protection for 3 months! i am going to enter and inspect this week.
As of today she is now 'asking' for the rest of the house to be skimmed, new skirting boards, doors etc etc. She is living in a bargain (£pcm). All this work would up her rent 50% on the open market!
As it stands today; i am 1 months free rent down, increased rent not paid and now requesting more improvements because she's embarrassed by woodchip etc.
Dilemma i have: can i send her a s8 (scare her) and s21 at the same time or is this legally not allowed? I dont want it to go to court (s8) because she's the stereotypical tenant who could win (single mother, teacher and i think with mental health issues (wouldnt sleep in the bedroom because it had woodchip even though shes lived there 14 years now). Our relationship of landlord/tenant is breaking down. Unless she agrees to market rate after any improvements or i want her out...

Basically can i send s8 & s21 at the same time?