My Mom finally consented to see a doctor for memory problems, but is now being combative. Any advice?

After a year of doing all I could to get my mother to see a doctor for memory loss, she finally made the appointment. After a private discussion with her primary care physician last summer, he would do nothing until she made the appointment on her own. Now that we are in the middle of the dr. appointments and testing process... she's taken the written test at the Primary's office, he ordered an MRI and now we are waiting to get into the Neurologist, she is threatening to cancel her remaining appointment. She is fighting tooth and nail every other day to call the appointment with the Neurologist off. She got furious when she saw that the reason listed on her appointment paper for the Neurologist states "memory loss" as the reason she is seeing him. She's completely in denial now of making the original appointment to her Primary herself for "memory loss." These tests and doctor appointments are making her more and more out of control lately, and since we have 6 weeks yet till the Neurologist appointment, my concern is that she is going to cancel. For example, just yesterday in a fit over a cell phone bill, she canceled her phone because "she had not used it in a month and therefore is convinced she does not need it. The real problem was that she had gotten a new cell phone and was convinced it was broken because she kept getting this message when calling a friend..."the person you are calling doesn't have a voice mail account activated" and neither my father or I could convince her that this had nothing to do with her phone. When the bill came yesterday, she flipped and canceled it. She's had a cell phone for years, so this behavior towards the cell phone was really out of character and in my opinion, an example of what I might expect in the next 6 weeks as this appointment that she is furious over gets closer. What do I do?