Tampa area...temporarily heating inground pool

My father-in-law is recovering from a stroke and is currently staying in the Tampa area with my daughter. He is at a point where he has regained enough mobility to get in pool and do some aqua therapy to regain strength and improve his mobility further with aqua exercises in my daughters inground pool (approx 25 x10). It is currently January in Tampa and pool water is only 65 degrees (unheated pool). We are trying to identify a temporary / rental heat source to bring the temperature of the pool up to a usable level for the next few months until we bring him back north. My daughter's home is a rental so we are not looking for a permanent solution.

While an electric heater may not be an ideal solution $$$ wise on a permanent basis we are thinking it may suffice for just the next few months to make the pool usable for him and might be the least involved solution to heat the pool with out getting into gas lines, etc. Again this would be just a temporary solution for the next few months so we are looking for an option that is least involved in terms of setup and operation.

Any thoughts / suggestions would be greatly appreciated. Also any possible source(s) in the Tampa area of a possible loaner / rental heater are most greatly appreciated by our family.

Thank you in advance.