[ossiblue]

I live in Cal. and have had similar issues. First and foremost, you need to know exactly whose fence it is and a lot survey will determine ownership. If it is on the property line, then you should get clarification from the city as to ownership/legal obligations as some builders divided lots with fences exactly on the line and they were co-owned. If the fence is shared and the neighbor doesn't want to contribute and has no legal requirement, your MIL can simply repair it at her cost or move it ever so slightly onto her property so it is clearly her fence.

If the fence is on you MIL's lot, I suggest she politely approach the neighbor and tell him she is having the fence repaired and ask if he'd like to split the cost. If he declines, she should simply do it on her own. If it is her fence, he has no legal obligation to contribute.

As far as the tree is concerned, yes, she can cut any part of the tree that overhangs her property BUT she cannot cause the tree to die or become diseased from the trimming. If it looks ugly, that's ok but if the tree dies, she is liable for damages. I think the suggestion that she ask the neighbor if she could have access to his property to cut the limbs back to the trunk is a good one. Again, if he refuses, she can cut them at the property line.