Landlord-Initiated Constructive Eviction in FL?

[Nathan R.]

Hey BP, I have a situation that I'm sure someone has some experience with, and any advice/suggestions would be appreciated. I have a SFR with a long-time tenant, but I am having serious plumbing issues and it is taking me way longer to fix than I expected. I have several concerns:

1) Right now the property is not safe to live in (there is potential and precedent for sewage flowing IN to the unit) and I'm concerned about health and sanitation issues. 

2) There is no lease currently in effect. The tenant refused to sign a renewal when it expired so there is some ambiguity about tenant/landlord obligations to each other (obviously the law applies - I'm talking about anything above and beyond that).

3) The tenant is difficult to deal with but has always paid rent (~8 years running). There are no eviction-worthy offenses (as far as I know - more on this later) and she has told me that she will never voluntarily move out under any circumstances.

4) The tenant is allegedly handicapped although I am doubtful whether she has any documentation to that affect. 

5) Besides the aforementioned concerns, I am also concerned about legal liability over the same concerns. Several times in the past, the tenant has threatened to sue over very minor [perceived] issues (such as talk about raising rent $25/month after 4 years of tenancy). 

Here are the actions I have taken or plan to take:

1) I have explained the plumbing problems to the tenant and asked the tenant to move out with incentives (last month rent free), and she became verbally very aggressive, including some threats which I do not take seriously. 

2) I posted a Notice of Nonrenewal of Lease today, with end of March as the last day. It's my understanding that with no lease I am only obligated to 15 days' notice although 30 days is "preferred." (Is this correct?)

3) I have started compiling notes and records of steps I am taking to fix the plumbing and correspondence to/from the tenant, in case lawyers get involved at some point.

4) If she does submit March rent I plan to cash the check, but not cash the April check if she sends it. If she vacates before April 1st I will give her a pro-rated refund of the March rent.

5) On April 1st I will file for eviction if she has not moved out.

Is there anything I am not thinking of? Have I completely shot myself in the foot by not threatening eviction when she refused to sign the lease renewal? If push comes to shove will my 24-day Notice hold up under scrutiny (timeline-wise)? Is there a way for a landlord to "force" a constructive eviction faster if the living conditions are unsanitary? 

As an aside, I am treating the plumbing issue as a completely separate situation and am asking for advice about that in a separate forum.