She is required to uphold attorney-client privilege even if her client pretends that privilege never existed.
More relevantly (putting her ethics and morality aside) prosecutors cannot profit from a breach of privilege by the attorney.
Even if she says, "I don't care if I lose my license to practice law, here's everything he told me in confidence", statements like that could not be used against Trump.
Trump's could potentially waive that privilege, but a court would certainly use a strict standard for concluding that. "She's not my lawyer" isn't enough -- he would have to actively post "...and even if she were my lawyer, I hereby waive any privilege from that non-existent relationship" for a judge to even consider it.