I totally get that .. I think at one point if my T had asked if it was okay to skip a session I would probably have reacted the same as you and then thought she didn't want to see me anymore. But now I would be able to say actually I would rather not skip one but sometimes it's so hard to say how you really feel in therapy isn't it.
Well done you on sending the email and it's definitely progress :-) .. I hope she still has the appointment available and comes back to you soon