Increasing strength and stamina post concussion

I have a new client who experienced a concussion 3 months ago. Neurologist advised either physical therapy or personal training and the choice is personal training. Strength training is a focus as muscle tone has diminished with the constant rest and inactivity necessary to recover. Increasing stamina is also a focus as this person cannot go for extended periods walking and running errands without getting tired. Client self reports no issues with balance although i suspect we will encounter some as we progress. Any advice from the community on specific exercises to include or avoid is appreciated. Thanks.