(Disclaimer: I just preparing for my first trail ultra, so anything I think I know is second source information.)

As I have understood, high mileage is not that important in ultras as it is for marathons, because ultras you are not limited by your aerobic capacity rather than your ability to withstand the pounding of up and down hills. ”Cat Bradley averaged 66 miles per week before winning the 2017 Western States 100”.

With that in mind, I’d not ramp up the mileage but focus on strength and muscular endurance type of training, with enough rest to let your muscles and tendons actually become stronger instead of risking further injury. Speed and tempo would be secondary just to help you retain good running form and quick feet.