Please step away from the Google....
Three is the classic age for kids to be very picky and, yes, even "controlling" in adult eyes - but remember, that's in your adult opinion. It is not uncommon, weird or a "diagnosable condition" to be three and to want what you want, the way you want it, THIS instant. I have seen plenty of kids this age do things like say "you have to sit right here while I do this" or "The blanket has to be put on this way and not that way and do it again until it's right."
Making the huge, unwarranted leap from the tiny handful of things you describe to worrying about OCD is only going to give you an ulcer. Stop the online diagnosing (where everything is geared toward scaring the heck out of parents over every tiny thing) and get some good books from the library on child development. A bunch of them. They will give you far better advice and be more reassuring than any "10 Signs Your Child Has OCD" stuff online. You need to read up (and talk to your pediatrician about) the stages that all kids, not just yours, go through.
At three, children are learning that they are independent beings with their own wants -- but they are still young enough that they have no idea WHY they want what they want, so your child probably can't sit there and answer you much when you say, "But why does daddy have to sit only there?" She may come up with something like "Becuase that's where my teddy bear wants him" or anything. Don't fear that she's OCD because she wants daddy there, or that she's hallucinating because the bear is telling her what to do. She's being three and trying to take control of a moment in her day. At three they want control of even tiny things because they know that the adults control everything else -- they are well aware that you tell them when to get up, what and when to eat, when you are all going out the door, when it's time to nap or play, etc. And they want a tiny amount of control. That is not OCD; it's growing up, to want to assert themselves just a little, even in something that seems insignificant to an adult.
Find out about the stage and you'll also get good advice on handling it. If you turn these little things into battles you are in for a nightmare and she will dig in and be more stubborn. Doing what she wants once will not create a spoiled or controlling monster. And telling her after the second rearrangement of the blanket that she's a big girl and can move her blanket around however she wants once you leave the room (and not coming back to fix it when she calls again) will not scar her for life, either.
Please do not compare her to the older children. Ever. As the youngest she may indeed try hardest of them all to control little things because she has not only mom and dad but also two older sibliings to run her day and her life. Expect it, read up on ways to deal with it, and don't obsess over OCD at this point.