Hi Kay,
I have a slightly different approach than most of the comments here, but you're here to see differening opinions right? In my view, you're in a classic scenario that a cost-benefit analysis will solve. We've been in this situation before...There's no correct answer IMO, though the obvious answer seems to be to 'get more money'. That does not always equate to 'raise rent'. To help decide what to do, I ask myself these question in the following order:
1) Are you currently producing cash flow?
2) How confident are you that you could get a new tenant in, that would treat your place the same and pay as consistantly as the current tenant in a reasonable time? What is that reasonable time frame?
3) How sure are you they will leave if you do raise rent, and if so, is it worth the cost of a month (or 3) of vacancy? Sometimes raising the rent a small percentage would take years of additional tenants for a few months of vacancy
4) What's the 'right thing to do'. Obviously you don't own rentals to lose money, but can you navigate the change in a way that is respectful and professional while still hoping to gain income?
Being a landlord isn't easy, because the decisions that come with it aren't. Numbers go a long way, and simple math is your friend in this situation. From my experience, people are blinded by the extra 50-100-200 dollars of extra cashflow a month and often don't realize that if you have a good tenant that pays regularly without causing issues, it would sometimes take another 3-5 years of a new tenant at the new rate to make up for the vacancy time of the turnover. In my experience, if you have an excellent tenant and aren't under water on the property, it's worth being upfront early about the need for an increase the next year or so, rather than springing it on them the time the lease is up. For us, it has created a better partnership and resulted in less vacancy, happier (and cleaner) tenants, and ultimately more cashflow and less headache.
I know it's not a direct answer, but I hope it helps your decision.
James