hide what from her? and I'm not certain what controlling the city has to do with anything.
Sophie says that Maenads are not smart and that they have already tried sacrificing shifters and weres, not vampires. Maryann must not really believe Sam is the one, she already had a shifter and killed her. From Maryann's interaction with Sookie, we see that Maryann knows that Sookie is supernatural, that is all that maenads require of their sacrifices, according to what we know of them. We also know that since Maryann doesn't know what Sookie is then it is possible that she has never met a fairy to sacrifice. The towns folk act as her familiars, I'm not sure what you were getting at with that. (I don't doubt that she wants Sam, I'm just saying the supernatural being that she needs to summon something that evil? probably requires the killing of something thought of as extremely pure.)
I misread wikipedia, I saw that she could communicate with her children telepathically and assumed she could read their minds. (Which as her children's maker, she could command them to tell her whatever she needs to know- not as instant as Sookie's power) Still it would make her far more powerful if she gained the other "half" of a telepath's abilities.
Sookie hasn't been in Bon Temp for awhile now and she has been after Sam the entire time. She seems pretty set on Sam. Remember when she was angry that the people thought they had killed Sam. If she didn't care about him and was on Sookie all the way, she would be indifferent to Sam.
Daphne was a shifter yes, but I think she thinks Sam specifically is the vessel. As in, the person, not the thing that God can come through. I think they think it is a specific person who is a were or shifter.
Having read the books, I am going to spoil a little.
Later in the books, Sookie gets a fairy godmother. She explains how she is a basic fairy from which all other elf and fairy type creatures emerge. Angels, demons, water sprits, green men, brownies etc.
I don't think it would be too hard for Maryann to run into a fairy of some type.
Also, I don't think the God is evil. It's supposed to be Dionysus to be honest. Maenads were Dionysus' hand maidens blah blah but he eventually left or whatever. Anyway, they don't see what they are doing as evil. If you listen to Maryann, she truly believes in this stuff with taking away humans inhibitions.
All makers can communicate with their children telepathically. Not actual words, but when they want them to come back to them they can do it in some weird way that their children knows and are compelled to listen to them. But Sophie has a extra ability to keep her children with her for as long as she wants. Most maker and children seperate very quickly after turned.
Anyway, I don't think she will turn Sookie, or Sookie would let her to be honest. Sookie is only still alive because she cannot read a vampires mind. If she could, they would have killed her fast. A lot of vamps have agenda's and less care for not killing someone, even if they would have to go before the Magister or their Sheriff, King/Queen.