Hi HildegardCrowe,
Firstly, I totally hear how stressed out and anxious this situation is making you. You are doing the right thing trying to resolve it by talking it out professionally.
Taking a step back for a second, I find it helps in these situations to try and see it from the other party's view, so that you can act accordingly. If your manager is new in post then it's likely that she will be feeling anxious about making an impact and will want to show that she is competent and credible with your team and the practice management / GP partners. She may also be wanting to 'make her mark' and bring in her way of doing things. She may be getting this wrong, but do you think this could explain any of her behaviour? If so, how might this help you in talking to her about the situation?
Can I suggest that if you want to stay in the job that you love and forge a healthier working relationship with your new boss, that you try to make the outcome from the meeting as productive and positive. Stay calm and try to put across your point in the way that describes how her behaviour is making you feel without directly getting into attacking her personally. So, for example: 'when you check up on my work I feel like I am being micromanaged where previously I've been given freedom to do my job. This is leading me to lose confidence in myself'.
I'm pretty sure that she will be feeling nervous about the meeting too, it doesn't bode well to come into a new job and immediately be having issues with valued staff members. They also won't want you going off sick for 2 weeks. So bear this in mind and feel confident in putting across your views in a fair, balanced way. If you can show some empathy for her position being new in post too (or even anything positive that you have seen of her so far??) then that could really help you get a good outcome from the meeting and show that you are being balanced and fair in your feedback.
Be clear going into the meeting what a good outcome would look like for you. How do you want things to be different as a result of the meeting so that you can continue to do a great job for the practice? Ensure that you share this in the meeting at the start if possible.
Try some positive visualisation - take a few minutes to imagine yourself in a meeting with your boss and her boss that is going really well. What are you saying, doing, looking like? What are they saying, doing, looking like? How does it end? Keep this in your mind as you go into the meeting. I do this as meeting prep all the time to embed a good outcome into my subconscious, you'd be surprised how much this helps me to have good meetings!
Good luck, let us know how you get on!