When to send to collection agency for non- payment of rent and break the lease.

[Mahmudul Shoikot]

I have a house in Texas and had to move to Michigan temporily for work purpose. I made a wrong decision of renting my house to a known person rather than going professionally with agency. 
Long story short, my tenant owes me 2 months rent and I have asked her to move out before her lease ends if she fails to pay the rent withinh certain date. So, as of now my understanding is she is moving out without having to file eviction. But, how can I collect my outstanding balance. How many days should I give her before sending it to the collection or if I can even send it to the collection? 
If so what is the procedure? If she says she wants to come up with payment plan, can I do that. What determines to send or not to send to collectiom agency?

Please help.