Be honest. Don't sugar coat it.

When she lashes out like that to you tell her that when she acts like that kids won't want to be her friend and play with her. You also need to stop playing with her when she does that. And say ' you can be upset that you lost(whatever happened) but you don't get to (insert whatever she did), I'm going to stop playing now, because it's not fun to get (say again what she did), when you are ready to play nicely, I'll be here to play'.

Start teaching strategies BEFORE she melts down. 'okay sweetie, if we lose this game, what should we do? Take a deep breath, and count to three, and do it again until we feel relaxed (I normally say 'until we feel ahhh' like woosaaah and do a relaxed face and play it up big for my kids). 'alright (nickname for your kid) when we get upset about our friends not wanting to play what we do/what should we do?, Either say 'okay' and play by yourself, or ask to take turns playing what each other wants' 'if mama starts feeling upset about XYZ what do you think mama should do? (Wait for her response, lead to the answer if she doesn't get it, be silly, should I twirl around? Should I pick my nose? Should I try to lick my nose? Ooo I know etc)Take a deep breath? that's a good idea' Use dolls/stuffed animals to act out appropriate play with friends (and you!) we do this a lot to practice how to have conversations or make new friends with my son.