Assuming your mom is not newly diagnosed -- she will want to continue with her usual precautions for summer which probably includes stay cool, stay hydrated, avoid fatigue. There are
cooling towels (Frogg Toggs are popular) that help one stay cool. She can get free ice water on request at any CS location; don't wait until you feel thirsty, drink/sip regularly. You say she doesn't need mobility aids, but a week at WDW is very different than life around home. She may want to consider an
ECV to help avoid fatigue and preserve her energy, essentially extending her day. Many people use a mobility aid at WDW who do not "need" one in everyday life. You might also want to plan for a mid-day break -- either back at the resort to rest or swim, or at least an ADR to spend some time inside with A/C. Hopefully others have some suggestions as well. Enjoy your vacation!