I just found this handy usb plant sensor to help me problem solve in the garden. While I don't have my yet, (I just ordered it from amazon with free shipping -- http://tinyurl.com/d4soz6 ) I have used my sister and it seems to do a good job both in figuring what is wrong and finding the right plants to grow in different locations.
The information from the product description is:
Once the Easy Bloom has gathered a diagnosis, plug in it into a USB port and the sensor data will begin to upload onto the computer. With three different modes, users are able to figure out where the best place is for a new plant (RECOMMEND), see how a certain plant is doing (MONITOR), or check if a plant needs to be watered (WATER).
Easy Bloom USB House Plant Sensor by PlantSense -- maybe the right techie toy for your mother for mother's day.