According to the Sixth Amendment, what can the woman do to support her court case?

A woman is accused of a crime. She says that she was nowhere near the scene of the crime. Her friends who were with her at the time are afraid they will be accused as well, so they refuse to appear in court as witnesses. According to the Sixth Amendment, what can the woman do to support her court case?

She can require the witnesses to testify.

she can require the witnesses to testify.