I think it's a good idea to cancel the next one, and (as you've said) let her know that you've had some realizations that you need to process. That's honest and makes a lot of sense. Then you've got time to reassess.

I completely understand wanting to avoid having her flip the switch on your therapy and end things. She does sound uncomfortable or unwilling to deal with the real issue you're having that she represents to you. So if she sees you trying to assess things for yourself, that might help put her on referral notions on pause. I think it's more important for you to feel in control of yourself in this situation, and if it somehow remedies a past hurt, when you didn't feel in control with your own mother, then yay you! That doesn't mean you won't seek therapy with another at some point, but if this one isn't working, then you can still walk away with something worthwhile by the way you leave.

I hope that makes some sense.