My DD is 2 years 8 months and has recently become much more selfish and possessive of toys and games she likes (no matter where we are, at home or other peoples houses / group settings). Previously, she would play alongside another child at toddlers who wanted to use the toy kitchen, not playing with, but not bothering them. Now, if someone comes near her when she is playing with something, she tries to get rid of them using whatever means she can. Usually this is removing their hands from an object, or (gently, but firmly) pushing them away. Once it has involved her throwing something at a child who was quite (good on him!) persistent about playing with whatever it was DD was using.
I expected her to go from playing alongside, to playing with.. not snatching and being a little terror.
I always remove her from the situation when I observe this behavior and she is warned and then given a punishment if she does not say sorry / does it again. So far, no sanctions seem to have had any positive effect.
I also praise her heavily and let her know I am very proud if she does (rarely) play nicely with someone.
She is about to start pre-school 2 mornings a week and I am worried she is going to become known as "that child" that you don't want yours to have to share pre-school days with because she is not very nice to others. God forbid, she might progress to actually hurting others to get her way. We went for a taster session recently, and honestly, she was the only one not able to play nicely in a small group (I appreciate she was also the youngest, so I am not really expecting her to behave like a 4 and a half year old until she is 4 and a half) but when do they grow out of this?! Is there anything I can do to help her learn social interaction etiquette (we read books and so on, but I do not think she can generalise to herself yet from stories very well) as they seem to have made no impact either.
Playgroup will probably provide a great learning curve for her! Not only will she see other children sharing, but she'll soon discover that NOT sharing makes her unpopular. A well-run playgroup will have strategies for teaching her to share and she will get it, eventually! So try not to worry! It sounds as if you're doing exactly the right things to try and teach her yourself and she'll learn! My son was just the same when we were out and about, even though he had to share toys at home with his older sister. He eventually got the message and I'm sure your DD will too!