Definitely do groundwork! There was a really bossy mare at our barn and ever since we've started groundwork, she is great! You can find lots of videos on youtube or you can go to clinics. Clinics are very useful because you can make sure you are doing everything correctly. Also, when you are doing groundwork, make sure you are confident. If you show any signs of being scared or 'weak' then the horse will try to take advantage of you again. When you are doing groundwork, the horse might be really naughty at first. She might rear, buck, kick, etc. but you have to stand your ground (even though it is very scary when a horse looks like they want to kill you!) It definitely pays off.
It sounds like she may be herdbound. If she is very dominant in her pasture, a horse can get uncomfortable when they are not in charge and do not want to be told what to do. Maybe see if you can get her into a different pasture away from those she is getting too close to, and lots of ground work and lunging to make her respect and listen. If she is calling out for her friends, make her work.
She also whinnies really loudly when I'm on board. She's not bucked or reared with me, only others helping me and doesn't do it to everyone!? She is super forward st the mo too whereas I used to ride with a stick!?
Thank you. Her tack was only fitted 3 mo this ago, defo not this although she has put on weight. She's napping, rearing when being asked to work work. There are certain traits she is getting away with on the ground with me but not much. She is bossing a 25 year old boy pony around now ... could her dominance be coming through this?!
Make sure you are stern with her on the ground first. If you or someone else is letting her get away with bad behaviour when handling it may translate to riding. Also check with your vet for any pain that could cause it