If you're forced to play by yourself, which I don't recommend, fear not. Sheva's ability is akin to Alyx Vance from Half Life 2. Unfortunately, she doesn't have quite the immunity that Alyx does, and can die quite easily if you decide to leave her alone with nothing but a pistol in a group of zombies while you run off to grab a green herb. (I learned this the hard way). Instead, teamwork applies. You watch her back, and she'll watch yours. Its not escorting, its not protecting, and I'm not sure what else to call it other than teamwork. Which is mostly what this game is based around. Find yourself at a locked door? You'll have to fling Sheva to the other side so she can get to it, while you cover her back with a hunting rifle.
Now, the best part is when you can play with a friend, or a random person on XBOX Live. I personally prefer using Sheva myself, the routes she is forced into at a split path seem to be more rewarding ammo wise, which as you might remember from RE 4, you will need to conserve ALOT of, or you are quite screwed. Anyways, you will find the game to be not only a tad bit easier, but alot more fun when playing with an actual person. Usually, and I mean USUALLY, cause there's some dumb people out there, the person will fare better on their own than the AI, meaning you don't have to stress about protecting them every now and again. Of course, the game has context sensitive melee moves that you must use if your partner becomes constricted, but even if you arn't near them the other player should be good about shaking zombies off on their own.
All in all, the game is looking promising, and if they never release an american/EU demo (which I don't imagine why they wouldn't) you should totally consider checking it out if you're new to the series. A few things might bug you, like not being able to move when you aim and shoot, or the turning which can be sluggish at times, but if you sit down with a friend and play it, I bet it is going to be a great game.