She has a house in California and changed her voter registration to her California address.
As long as that is the case before she takes the oath of office, I don’t think there is a law to prevent her becoming a senator representing California.
When did she buy the house?
If there ever was an example as to why the 17th Amendment should be repealed this is it!
The California State legislature would likely choose an ass but at least it would be a California ass.