Mother Of The Bride

As of how she gets to the ceremony there is no hard and fast rules. She can either travel with the Father of the Bride, if they are together or with her escort if she has one. If not, and the bridal party, bride and MOB are getting ready together then the MOB can travel with them in limo or whatever. Just remember that however she gets to the ceremony, she still needs to get to the reception and then home that night!
As far as walking down the aisle, the Mother of the Bride is the last before the bridal party starts down. Usually it will go, Grandmother of Groom, Grandmother of Bride, Mother of Groom, Mother of Bride, then the bridesmaids, Maid of Honor, ringbearer,
Flowergirl and ta da da da the Bride! Don`t worry though at your practice your Pastor, Priest, or coordinatior will have you all practice it.
As a side note, my brother was my husbands Bestman. So we had my husband (the groom) walk his Mom down and then my Brother walked my Mom down, everyone commented that it was so nice to see that done that way. At first our Pastor didn`t want to do it, he thought the usher should walk them down. But then he said it would be OK. After they walked them they went to the alter and then the bridal party started down. It worked out. So even though alot of tradition dicates the ceremony there is still little things you can do to make it your own! Good Luck and have fun planning!