My wife has covid with sats at 89 t0 91. would you recommend hospitalisation?

Go to Emergency: Oxygen saturation levels below 92% require emergency medical evaluation. Take her to the local Emergency Department for a thorough exam and appropriate lab tests, etc,

Low O2 sat: Those sats are low and may well reflect covid damage of the lungs which occurs relatively early in the infection. Does she manifest respiratory distress or chest discomfort? Nevertheless I do recommend hospital evaluation,testing and rather intensive treatment, if indicated, including oxygen administration. Call your physician for detailed instructions.