H.W.
From my preschool teacher perspective, I think your daughter needs a little more help from you. That's why she came to you, right?:)
In my experience, children at this age come to us precisely because they need help. At four or so, kids really don't know *how* to play fair. This is what I would have done:
Go to all the girls. Tell them what you see. "I see you two are playing with these toys. Are you having fun?" (Give them a question to address *them* before continuing. Get their attention. Wait for an answer, then continue.) "(Daughter's name) would like to play with you. Could you please show her which toys she can play with?" This puts the children who are not sharing in a good spot: they are getting information that they need to share the toys, and you are asking them to be specific, so they do get to pick.
Exclusion is very common at this age. Working as a preschool teacher, a great deal of my work is social coaching for kids. We have to be present and tuned in. One wise woman said that when you let very young children 'work it out for themselves', it's often the bully that prevails.
It's good to narrate (using descriptive language to talk about what's happening), to offer options (such as "can you find the toys so-and-so can use?) and then, yes, to help our own kids move on when the other players are not going to budge on not-sharing. At almost four, your daughter doesn't understand the idea of 'taking the high road' and finding something else to do. She just knows she wants to play with the toys, is being excluded, and feels sad.
Your daughter will eventually learn how to 'handle' situations like this, but it doesn't come organically. From my experience, it comes from repeatedly giving them help, giving them language to ask for what they want, helping them problem-solve. Kids this age really cannot do this on their own, for the most part. I think you explained the incident with the video/dog pretty well ("Do you see that the other kids are watching a video? I think they want to do that, and you can play with the dog if you want, also. That would be fine.") I want to be clear that I'm not advocating 'helicopter parenting'. However, from what I've seen with my preschoolers, when they are asking for help and we tell them to go figure it out on their own, kids tend to get very confused. They usually have tried to solve their own problem, and now need a bit of extra help. So the next time your little girl comes to you in this situation, take that time to teach her what she needs to say/do to reach her objective.
Of course, as I said, there are some kids that are not going to play nice, no matter what, and then you can help her to move on to something more pleasant. But do step in and help her with the language around her requests to play/share. She needs this a lot, and will likely need this for quite a while. I've seen 6 and 7 year olds who need help figuring out how to ask those "can I play" questions. Your daughter is not alone in this-- very age-appropriate!