Oh boy, welcome to the life with a 3 year old!! I had 2 at once...........sounds like she is jealous.......here are some recommendations.
1. Let her help with her brother, fetching diapers, picking out clothes for him, etc....
2. Find something special to do with her during the day.......for a half and hour or so....something she likes, maybe when he is napping.
3. 2 minute time outs are not long enough.......is her room safe for her? If so, send her there when she misbehaves.........if she screams and yells, don't let her out until she stops.
4. Talk to her about being a big sister.....she's young, but she will get it eventually what that means.
5. Tell her you love her, only when she is being good.......so she gets praise and love when good, not when bad........
As for your parents, the same thing must apply.......sounds to me like she wants attention......so, if she isn't doing anything to hurt herself or someone else, ignore her when she acts up............if she is hurting someone else, remove her from the area and the issue...........by putting her somewhere where she is alone for being bad, that should stop the issue......eventually.........
You can do this, and you can take control, just be consistent, loving but firm.......everyone who watches her that goes through this must be on the same page..........so make sure you all share stories and what works.
Hang in there........take care.