2 tenants one abdoned

[Holly Buell]

I have a 2 bed rental in the resort area of the mountains. Tenant A has been living in the unit for several years and I went to college with her. Tenant B just up and left without notice, she has paid though the end of the month but all her stuff is gone. I'll reach out to Tenant B to make sure she has left but what are the other steps for eviction if only one tenant has left without notice? 

I charge under market rent for the unit and Tenant A knows this and wants to stay but is difficult to live with and she cannot afford to live by herself. I feel like every 6 months or so she gets a new roommate and there is always drama. Can I put her on the lease as being solely responsible and she can deal with her own roommate issues? Could tenant A create a document type lease for her roommate? What are the pros and cons and liability here?