I am filing CA state return and a little confused with Community Property Laws and when these apply. I am filing a joint return with my spouse and she is not CA resident (but I am) but lives in another community property state. Does it mean that 50% of her income is still CA taxable because of the 50%-splitting?

I see a lot of examples of how to split income for spearate filing but not sure it also matters for joint return.

No. If your wife did not earn her income in California, then California has NO claim on it for income tax purposes.