17 Month Old Screaming at friends....help!

First, purchase some spongy ear plugs and keep them handy. When she screams in that high pitched scream insert them.

This is a phase. Toddlers are possessive and do not like sharing. They do not like sharing toys or attention. Screaming is one way she knows to get her point across..
Until she learns her words for her feelings, this is one of the ways she will express herself.

The main thing you can do is, use distraction. When she starts screaming, try to divert her attention. Pick her up and turn her in a different direction. Start singing a song or clapping.. Turn on some music and start dancing.. Keep a couple of toys handy that were not in the original pile she was possessing and see if she will switch gears.

Turn on and off the lights or open and close the shades.. Make it a different situation all of a sudden.

Also try to give her the words.
"You seem frustrated." "You seem angry."

Practice sharing.. It is a little early, but if you initiate it, maybe she will catch on..

Sit on the floor with lots of toys that are similar.. Like blocks. Place both children there.. build a small tower, then offer to share. "Will you share my block?"
"May I share your block?" "I like when you share." "Can you share with Mary?"
"That was nice sharing" "Mary can you share with Suzie?"
"Suzie that was good sharing. Who will share with me?" "Thank you for sharing."

The other good thing to practice is trading. "May I trade this red block with you?"
"Will you please trade your blue block with me?"

"May I play with the doll in 1 minute?"

Like I said at this point it will seem fruitless, but you will be amazed that if you keep up this type of chatter they can catch on pretty quickly..

I am sending you strength.

She's really at the wrong age to make much sense of sharing. Or for time-outs. It's fine to introduce the idea and interact with the children in "sharing mode" for short periods of time – that's how they will eventually learn. But she's right at the age when it's becoming clear to her that she is a separate person with separate desires, and this is compellingly important to her. Plus, there's that small problem of kids that age having short attention spans and very little impulse control.

Rather than trying to insist the children play peacefully together for more than a few minutes at a time, put some sort of barrier between them so they can each play with "their" toys in their own territories. Allow them to visit and play near each other only as long as the results are peaceful.

Your daughter's pinching and biting is an unsurprising response to painful and upsetting screaming in her face. She wants it to stop as badly as you do. Foam earplugs might help you, but your daughter isn't likely to tolerate them. So do all of you a favor, and avoid the situations that become too stressful for all of you. This phase will pass, and probably faster if you don't allow it to become reinforced through repetition.

My two boys were 15 months apart in age, so I bought two identical toys of every toy so they each had their own. If I didn't have two of each toy, I didn't put it out for play. I even got the same color so they wouldn't fight over that.

Developmentally this age child is just discovering they are a separate person -- so sharing doesn't make sense to them -- neither does time out. Consider setting up separate shelves for each child with their name on them and with identical toys stored in each shelving unit with each toy having its own space on the shelf. I outlined the toy shape with masking tape on the shelf so the child knows where to return the toy when they're finished playing or you can encourage and help them by showing them how to store the toy in its place on the shelf.

Another thing that helps is to use rugs that define each child's space for playing--so Ann has her own rug to play blocks or trains and Amy has her own rug. Get a sturdy, tight weave rug (the kind that's used for wall to wall carpeting) about a 2 x 3 foot piece that you can roll up and stand on end next to the shelving unit, then each child can be shown how to set up and put away her own place space rug. Set the rug in a plastic bucket along side each child's shelving unit to keep it from unrolling.

For the next two years, the girls will need their own play spaces and toys as they are learning the concept of me and self. That's why they're always saying mine -- they're telling everyone that they are a separate person from you.

I know this sounds lame, but I had to tell my daughter to use her words all the time. She would cry or scream in frustration and we'd go "use your words" and eventually she would talk more. It is frustrating time for all parties involved. I really feel for you! You almost feel helpless, right? At least you have a good support system on your side. :)