Legal Question in Personal Injury in California

Unless she has a restraining order or she is the guardian/conservator she has no legal control of the situation

If the boyfriend is incapacitated and the boyfriend's mother has a power of attorney for healthcare then she decides what she feels is best because she is legally speaking for the boyfriend. If she does not then the next of kin should be the son who is an adult and would decide who is allowed to visit the boyfriend. The girlfriend (your daughter) is not family at all even if she is the mother of a son with the boyfriend. Therefore, the person authorized to make decisions for the boyfriend can bar her as a visitor. People who are not married need to think about all these issues that might come up during the relationship and do the legal paperwork before those issues come up. Simple forms are available free such as the power of attorney for healthcare purposes. Kaiser has a very good one in its website.