advice needed on a tough choice

[Megan A.]

My husband and I purchased a duplex in July 2015 and inherited a wonderful renter who always pays her rent on time. She never causes any problems and is a quiet person to live next to as my husband and I have moved into one side of the duplex to update it. Our renters lease ends September 30th and she has voiced that she would like to stay another 6 months because she is saving money to buy a house. Now for the problem, we bought and moved into this duplex to build out the unfinished basement on our side and add a bedroom as well as a family room in order to charge more for rent. We are almost done with the project and we're hoping to move into our renters unit to do the same thing starting on Sept 30th. The financial breakdown looks like this: -Our renter pays $1,025 (she has a 2 bed/1 bath) -Our mortgage/taxes/insurance/PMI-$1,520 -Market rent for a similar property for a 3 bed 1 bath is approx. anywhere from $1250-$1450 in our area. I am confident we can get at least $1300 for our updated unit but potentially more. -We have done all remodeling/updates ourselves and have spent approx $5,000 -We do all maintenance ourselves and our renter pays all of her own utilities. The dilemma is, do we let our great renter stay another 6 months even though we could be renting our updated unit out for $300 more a month if we moved into her unit in September? It's scary for us because we haven't had to go through the process yet of finding a new renter so what if we can't find somebody or what if we end up with somebody who doesn't pay rent on time? There's also the part where we will have 6 months where we really can't do much work to our renters unit so the whole project gets put on hold. Our goal is to fix the other side up and then move out. I am confident we can be collecting at leastz $1300 per unit at that point. We also may be able to refinance this summer from an FHA loan to conventional to get rid of our mortgage insurance. We have to run the numbers to see if that even makes sense to do or not because interest rates have increased since we purchased our home. Does anybody have any good ideas or advice? Thank you!