Hi Brady,
If you are looking at it from just from a dollars and cents perspective then you should keep the tenant. I am going to guess that you have checked the comps for the neighborhood the house is in and you have found other houses for rent at the market rate?
If the rent payment covers your mortgage and you have a good tenant, why would you get rid of them to take on the expense of unit turnover, because you will have to do one, and the 5% vacancy loss just to increase your rent $150 per month?
I would also find out from your friend if they have increased the rent since that tenant has been in the house. Instead of getting rid of of the tenant - increase the rent slowly. At lease renewal increase the rent $50 per month and then the same the following years until it is at market rate and more than likely the tenant will leave on their own and you will have still gotten the rent for that entire time until they moved out and built up your reserves for that property.