Lilianne is beginning to develop a fear of strangers and will reach for her mother when she sees someone who is unfamiliar. it is likely that lilianne has also just

It is likely that Lilianne has also just developed a sense of object permanence.
Object permanence refers to the fact that infants know that certain objects/people exist even though they cannot see them at the time. In the beginning, infants might be scared of meeting new people because they still don't fit their existing schemas (they are still unfamiliar with them), but once they get acquainted with that person/object, they will no longer be scared of them, which will happen to Lilianne as well.