Mother of 6 died. We took in her 17-year-old. We did not become legal guardians. She is 18 and in college. Can we claim any of the expenses we have provided for her?

In November 2017, a mother of 6 children was in an automobile accident and lost her life. My husband and I took in one of the children---a 17-year-old. Because she would turn 18 years old in less than a year, we did make any attempt to become her legal guardian, foster parents, or to adopt her. We did not claim her on our 2017 income taxes. She is now 18 and a freshman in college. Can we claim any of the expenses we have provided for her?