Enjoy the time you have left with her. When my mom passed I got a call at 5 in the morning to get to the hospital . We did not have a chance to say so long , still have guilt for not seeing her that week before she passed.
When my good friends lost their son to MD a month back , (they were devastated and still are) they had no idea what to do next.
Your mother is helping you in a big way by going over the funeral plans now. You will not second guess what she would have wanted because she has talked with you about it. Now you will not second guess what she wanted and you will know were all the important papers and such are that you will need. She is being very strong for you right now. Write things down for yourself when she is talking about it .