CL, yes you should tell them. They are not going to send you to hospital or lock you up because you have suicidal thoughts, far from it. Suicidal thoughts are normal for PTSD, and especially medicated. Without you saying it, your doctor already knows. What she is looking for, is your honesty so that she can measure how severe they are, whether you need a med change or more appointments need be introduced. Her questions are far from wanting to lock you up just because of suicidal ideation. They don't lock people up just because of suicidal thoughts, or send them to the hospital.
Don't be scared to be honest with your doctor. How many people here I have been through this with already, I could not count, but each one once they come back and say they have been honest with their doctors now, most are getting better support and direction in where healing needs to go. Physicians are not mind readers, and if you are not honest with them they cannot move in the right directions. You MUST be totally honest with them, and not fear things like hospitalization or the like, because that is not what they are about. They want to get you better, but unless you are honest, they can't help you to the best of their capacity.