Greetings! My sister and I will be flying into Phoenix from different destinations on a Thursday night in September and will have a night and half a day to spend before our accommodations in Sedona are available.
She was thinking about staying that first night at the Saguaro Lake Ranch cabins, and a trip on the Desert Belle Cruise around the lake.
Other than staying in downtown I am looking for what other one night/half day ideas for this area y'all could offer us! (Note: she doesn't hike or do horseback, darn it, so those two things are out!) Thanks!!

Take your pick between the Heard Museum and one or more things in Papago Park including the Phoenix Zoo and the Desert Botanical Garden.

If the Grand Canyon is not already in your plans, that would be the perfect trip to combine with Sedona. Spend the day/night there on Friday, take a leisurely drive to Sedona on Saturday afternoon to check into your accommodations there. Obviously the Grand Canyon is not 'Phoenix area' but it makes sense to combine it with Sedona.

If the Grand Canyon is out, drive the Apache Trail on Friday - stop at Tonto National Monument and the Boyce Thompson Arboretum along the way. That can take half a day or more. Visit Heard Museum on Saturday morning then head to Sedona.

Visit Frank Lloyd Wright's Taliesin West. https://franklloydwright.org/taliesin-west/

The Heard Museum and Taliesen West would be excellent choices.