Rehab and raise rent OR avoid turnover costs?

Hi, everyone! I bought a 3/2 SFR (C+ class) last October for $55k with a 5 year tenant. I raised her rent from $765 to $800 in January on a M2M. I was originally planning on lightly rehabbing the unit (5k) this spring and getting a new tenant at market rate which is $1000-1100/mo but I now have 2 other rehabs that are coming up at the same time (my first investment rehabs!). My tenant is a single grandmother w custody of her 2 year old granddaughter and cannot afford more than $800/mo. She has been a great tenant and gives me rent checks a few months in advance. I am thinking about keeping her there for another year at $800 to avoid having to spend the 5k this spring and also avoid having 3 units turning over at the same time! I realize I will be signing up to lose $2400-$3600 for the year in rents leaving tenant there at $800 but it does put me ahead of spending 5k and having 3 vacancies at the same time. What would you guys do in this situation? Any help on this would be greatly appreciated!! Jackie Botham, GR, MI