I guess it is a part of growing up. Learning to socialize, to share, to play together. Even as i see Eliza's 4 & 6yr old cousins play, they're still learning! A lot of times we have to mediate between them and guide them to play without ending up in a fight or a load of complains.
I wonder if it's some of Eliza's experience with other kids who are younger than her, that she was very protective over the things she plays, or it's a developmental phase. She doesn't like to hang around younger kids or sometimes kids her age, as if she's wary that they will take the toys she's playing. Then she'll get very upset about the whole situation.
Or she'll take what a younger kid is playing and a whole tense situation will ensue as we'll be disapproving of her actions and get her to return the toy which she'll throw it or hold on even tighter.
Most of the time it ends in tears.
Now, what helps is to prepare her for the possible situation when some sharing while playing together is required. We help her to understand that she can say no to another kid who wants to take her toy or she can give the toy. And when she wants another kid's toy, to wait for her turn, to ask or to find another better toy, or to play together (a concept which i think will take a while to master).
It's not that she doesn't play nice...she'll generously pass a toy to another kid when encouraged to and when the kid isn't being mean or threatening to her. I've seen her wait really patiently for a little boy to finish playing the train tracks. The boy was playing forever...and when his parents tried once to distract him away he almost broke down. But Eliza continued to wait...she told herself, "wait for train". I think the parents was paishe that she was waiting so long that they eventually carried their son away from the toy to something else, not without protests from the little boy.
With some practice, with some guidance, with some wisdom, may God grow her to be a good friend, a kind and loving one.