Ask Mr. Smarty Plants

The species that generally occurs in California, Maytenus boaria, is not native to North America and we are supposing that this is the one that you have. Although our focus and expertise here at the Lady Bird Johnson Wildflower Center is on plants native to North America, we are happy to point you to advice on non-native plants if we can. This Urban Forest Ecosystems Institute article on the Mayten tree  indicate that the tree needs good drainage. Another urban forest group, Canopy, based in Palo Alto, California, lists "collar, foot and crown rots" as problems for the Mayten tree which certainly could occur from not having good drainage.

The California Invasive Plant Council lists the Mayten tree as very invasive and potentially damaging to infrastructure, like sidewalks and foundations.  Since it is isn't flourishing anyway, and is both non-native and invasive, your friend might consider taking it out and replacing it with a tree native to the Santa Clara County area. Here are some suggestions from our Native Plant Database:

Arbutus menziesii (Pacific madrone) - pictures from Google

Cercocarpus montanus var. glaber (birchleaf mountain mahogany)

Quercus agrifolia (California live oak)

Umbellularia californica (California laurel)

From our Native Plant Image Gallery: 

Cercocarpus montanus var. glaber

Quercus agrifolia

Umbellularia californica