J.J.
hi C.;
you got a lot of interesting advice but i feel i want to offer this perspective as well; i don't believe that any amount of 'reasoning' or logic w a 2.5 yr old will work at all and it will just make you more upset.
my kids are 3 yo boy and 18 mo old girl. my son went through terrible jealousy and a lot of awful acting out between 2.5 and turning 3; we also were moving at the same time to a new apt. and we were all very stressed out. his behavior included the same things you describe about your daughter, plus random hitting of other children, starting fights, hitting the baby, terrible tantrums, etc. and this was all coming from a very verbal, loving, fun, bright child.
but smart as he is, no amount of talking about it did any good. and it actually made things worse. children this age have the attention span of a flea. after you hit the second sentence in your explanation they are already irritated and distracted.
consequences are fine but i really suggest controling the enviornment and not putting your child in situations she can't handle. some people say, "Oh they have to learn to socialize," and that's true, and they will learn; they just might need to wait another year or two or three. Or they might just need another 6 months. How bright or great your child is has nothing to do with how fast they will mature socially.
What i do w my son is i just don't take him places or set him up with things where i know he'll be overwhelmed; for example, birthday parties. he loves the idea of them, totally can't handle them and gets overwhelmed and hits. so what i do is find out in advance roughly when the mom thinks they will be doing the cake, and we go very late to the party, like 20 minutes before cake time. bring a present, play a tiny bit, sing the song, which is his favorite part, have cake, and get out of there. or as you describe, the beach. we go very early in the morning, like 9, because that's his best time of day. the more tired he is the worse he is. we bring a bunch of toys of our own, but he usually only wants other people's stuff. i give him one or two chances to play nicely and share, and if it doesn't work, then we just stop playing with other kids. i say, "Ok, we're just going to play with out own things way over here today, that's all." and that's the end of it.
because the problem is this; no matter what kind of discipline you use, and i would strongly urge you to read "1-2-3 Magic" and consider using that system when your daughter is a little older, ultimately, for bad behavior there are consequences, and how far do you go? do you leave the beach? i for one do not want to pack up all the beach gear and go home and ruin the day, although i have done it; but you have to be willing to back yourself up and go that far, because idle threats are torture and mean and make you look foolish. if you can't back it up, she'll figure that out.
the kids all mature eventually. my son is slowly learning to play better with others. i am confident that eventually, he will be able to do this; he's not going to go to 6th grade saying "no mine!" and it helps me to not compare him to other children who are more laid back. that just makes me feel bad. he is who he is, as your daughter is terriffic on her own terms.
try not to worry. don't make it bigger than it is and give youreself a break. don't get frustrated and anxious, just manage the circumstances and make it easier on your own self. the less anxious you are, the less anxious she will be. really.
also i would urge you not to label your daughter 'out of control' to others or in your own mind; she's not at all out of control, and this identification will make you feel worse about her and have more panic about the whole thing, which will make her behave worse. she's really normal. give her the room.
good luck!
J.