You do not have to have a reason for cancelling sessions. I do not think it is a good idea; you cannot work on a relationship by yourself, what you think or feel someone else will think or feel is not what they think or feel! Only they can tell you what is going on on their side. If you want to take a break though, just call her office and cancel your future appointments and tell her you will be in touch if you decide you want to return. If she asks "why" you say you want a break to work on some things on your own and you thank her and say "I'll be in touch" and hang up. What she thinks is what she thinks; you cannot have any effect on that, it's hers.