Other people have given you good advice, so my first advice is that you take it to heart. My other advice is this:
1. Be realistic about what you have to offer your preceptor. No, REALLY realistic...really really realistic. It is a good idea, I think, if you ask various midwives (such as here, or other forums) to give you an assessment, to help you be realistic about your 'place' in the scheme of things, given your current state of learning and experience with birth.
Much the same is true for doula training--though of course being a doula is different in many ways from 'med training', and as others have pointed out, doula training and work can be useful on the path to midwifery. But the rules are different for mws and doulas--a doula is not really responsible for the health/well-being of mother and baby the way a mw is. So, some of what is learned in doula training will also have to be set aside; your view of your preceptor and her actions/choices with clients cannot be tainted by rules that apply to doulas but not to mws.
It is a good thing to honor your prior learning and experiences in birth work (or related, such as nursing). It is a good thing to have *some* ego, some self-esteem, good to view yourself as an equal to all beings, deserving of respect, kindness/courtesy, and to be given the training you seek in an exchange with your mentor. And yet it is SO important that you are realistic about your book-learning and experience--that you keep a healthy sense of proportion about all that. As 'an equal to all beings', you certainly have the right to ask questions, speak your opinion, etc (in appropriate, courteous time and fashion!)....but you must be prepared to accept new information and perspective. You must be mentally and emotionally prepared to have your assumptions challenged, and to be critiqued as a student without taking that personally. You may 'become friends' with your mentor, but she MUST be your mentor/teacher! And she must, for her own survival, do/say what she feels is needed to protect her own reputation and working relationships w/clients. COnsider how well (or not) you currently take critique--ask your loved ones and former instructors for an honest appraisal of this.
Anyway--be realistic, be open, be ready to be a student including ready to be corrected/critiqued. Know that you cannot expect your mw to treat you with kid gloves, walk on eggshells around your sensitivites--though you will always deserve courteous treatment, even in being critiqued. If you run off with hurt feelings/outrage over a critique--well, that will be about YOU, not your mentor. And believe me, you will most certainly NOT be treated always with courtesy and kindness by your future clients if they are upset about something!
2. Communication is HUGELY important!!!! For you and your preceptor, for you and her and clients....really, for you in your relationship with yourself and with everyone in your life. So take it seriously, take comm courses of various sorts, or read books on communication and practice the skills and theories involved. You can look into NVC (non-violent comm) or any number of others. Communication is HUGELY important in this work. It is a subject to learn and a set of skills to practice just as avidly as any other more 'science-y' subject of midwifery.