Does the questioner bear responsibility for her friend's departure from Islam if she severs ties with her, knowing that advising her might worsen her condition, and that remaining with her might jeopardize her own religious commitment?

If associating with the woman causes you harm, then there is no sin in cutting off the relationship with her. The scholars have unanimously agreed on the permissibility of a Muslim abandoning his brother for more than three days if he fears from associating with him that which would corrupt his religion, or generate harm in his religion or worldly life, due to the Prophet's (peace be upon him) saying: "There should be no harm nor reciprocating harm." It is advisable to seek some righteous women to advise her.