rent arrears

Tenancy Types and Management

Hello,
I have a tenant who has always been late paying her rent, but usually phones or we can get hold of her. This month she hasn't paid it at all and has gone to ground. I think the time has come to get rid of her, but I would like to know the quickest route.
Originally I was going to simply give her two months notice (section 21)to avoid anything confrontational, but is it quicker to just issue a section 8 for rent arrears once she has missed next months payment aswell?
Also, if she doesn't pay the outstanding amount (which is fairly likely!) is there any way I can get that money back from her?

Thanks