my dd1 is EXACTLY the same. if she isnt the first person out the door, first person to get in the bath (if i put her baby sister in the bath first), if she doesnt get a certain butterfly plate at mealtimes, if she doesnt have her skirt on a certain way (belt loophole has to be precisely under her belly button), if she doesnt get her milk up to the fairys wings on her bedtime cup, if i dont hang her towel up on the 3rd ring from the left, if she doesnt wipe her bum 3 times after a weewee and 4 times after a poo, she gets VERY upset.
i spoken to a few other people who have children the same age or older, and they all (well most) agreed that at this age a lot of children are like this.
it seems to be a control thing, they dont have much control over their life (we tell them what they are having for tea/when to go to bed/etc, so they try and exert some control over things they can, like what they want to wear, how their toothbrush should be placed by the sink, how teddy should lie by the pillow, etc.
i try and help dd1 with her little things as much as i can, try turning a few into games, and she is mostly happy. i just try and tell myself she will grow out of it.
i think dd1 here gets a bit upset if things go 'out of control' in our house occasionally, ie if dd2 gets tired and we put her to bed early and have to change little plans, and i think its sometimes too much for dd1 (in other words, dd2 can upset the balance in her life)
to dd1 routine is very very comforting, and i think its true for a lot of children this age
just try and go along with her little control things and dont worry too much
if you cant stop worrying, talk to a professional to ease your mind
hth xx