I have dealt with this. I'm 37. I no longer stutter, but I stuttered until I was 36. Always talk at a rate that is comfortable for you. Get used it. Don't rush your speech for anyone. If she just looks irritated, ignore it, and continue. If she actually tries to speed you up or cut you off, stop what you're saying and ask her why she is doing that. Get her to think about what she's doing and why she's doing it. If she responds that you talk too slowly, let that be the gateway into discussing why you can't talk as quickly as she would like, and that it shouldn't be about speech that's comfortable for her, it's about what's comfortable for you, and you shouldn't be expected to do something that you physically can't. No one should.