Lady Margaret should have told her son that Myra was in...(Spoilers)

She knew the girl was deeply ashamed and troubled and could have prevented her from leaving if she let Roy know about the situation. Of course there is no way she could have predicted the suicide but given that she let her down before the smarter thing to do was get the poor girl some mental help. She should never have listened to Myra and her request when she knew she was unstable and fragile with all she went through thinking Roy was dead.

I bet she was wracked with guilt after that and Roy wasn't thrilled with her.