Does my client [name withheld] have a safety risk when interacting with [name withheld] who is an MK Ultra victim?

This will be a potential hazard because both individuals are under watch so any unauthorized interaction between them will be suspicious and will increase scrutiny. This you do not want to happen because your goal now is to become irrelevant to them, so they will have lost interest in following you to note your whereabouts and activities. You have already referred her to your channel as a source of help, so you have done right by her and need not feel any guilt in bowing out with respect to further contact.