Tenant rights when wishing to sell

Possession - Section 8 and Section 21

I am considering selling one of my tenanted properties to help fund the purchase of a new PPR. The tenant has been in situ for over 5 years with a mostly good payment record. She is a single mother with 2 children of school age. She has just lost her job (contract teacher) and has advised me that she is starting to run into financial difficulties until she can find another job so is only able to part pay her rent.

What rights would she have to stay in the property if she cannot afford to pay her rent? Am concerned that I will have trouble selling it is a tenanted property to an investor if she now has a poor payment record. If I give her notice to vacate, she may be difficult to evict? I don’t want to cause her more stress or be unreasonable, but would be good to know where I stand on this. I do believe she could be difficult so would not indicate my intentions until I am clear on what I can do.