You should expect her to take a bit more time with you than maybe she does with her nonpregnant patients. You should, at every visit, tell her about the specific location of your aches and pains (even if she doesn't necessarily decide to adjust that area). I normally don't ask my patients about their pains at every visit, but I do ask my pregnant patients.
You should expect to let her know about everything that is going on with your pregnancy, whether you think it will affect your chiropractic care or not. It doesn't just have to be pain. At each visit, let her know about all changes in your body, how the baby is feeling, your emotions, etc., even if you don't think it significant or abnormal.
You should encourage your other prenatal care providers to work with your chiropractor and to share information. I regularly communicate with my patients' other providers, with my patient's permission of course. (If you have a care provider who is against chiropractic during pregnancy, just take it with a grain of salt and realize that he/she does not understand chiropractic. Some, esp some MDs, think they know but were ill-informed.)
You should expect to follow her recommendations for your care and not just go when you think you need it. Depending on your case, she may want to see you less often or more often.
And most of all, you should expect adjustments to be gentle. She is obviously experienced in adjusting pg women, so I imagine it will be very gentle and comfortable. It is most often much easier to adjust a pregnant woman than a nonpregnant woman. There are many ways to adjust a pregnant woman, such as with a drop table as noted from PPs, with a pg pillow, with elevated hip pieces, on the knee-chest table, with an Activator, etc. You should tell her if a particular position is not comfortable, as every person is different.
You should expect to be very proud of yourself for taking such a positive step toward your health (not just pain relief!) and that of your baby. I'm thrilled for you, and I hope you let me know how it goes!