I was going to say as above get some games where she has to wait to take her turn. Our 3 year old loves snakes and ladders, connect 4, dotty dinosaurs (loads of the orchard games). If he had friends over we would discuss before what toys he wanted to share with his friends and what toys needed to go up to his room (special toys). We explained over and over that these were toys he was happy share etc. it worked pretty well. We will do that now, if I know he wants to take something to a friends house that is a prized toy - I say do you want to share it? Because if you take it you have to share etc. he is now pretty good
Yes it's an age thing. She'll grow out of it. I'd say don't demand she share with others because as an adult if I have something and someone else comes along and immediately tries to take it off me, I'd be annoyed so I completely get why a child would be very upset if someone else comes over and interrupts their play to basically steal something they're playing with. Instead teach your child to say, "I'm just playing with this. You can have it when I'm finished." And I encourage my other daughter if she wants something to say, "Can I have that when you've finished please?" rather than jump right in and try and grab everything.
That's exactly what we have done Rebecca, honestly changing the language around things at this age is a game changer! I also second the orchard toys games, my son loves them and it's really helped him come on in many ways because of the variety x
Yeah we had this for a bit, songs about sharing (cocomelon "wait your turn", annoying but helpful). And we bought a pairing game and played it at home and really emphasized who's turn it was, to try and help. I think they all go through something similar.