My mare had this same issue. It sounds to me like she's herd bound, she wants to be with her horsey friends and you're just a little pest trying to make her leave.
The first thing I'd do is spend some time becoming part of her herd, so she wants to be with you MORE than with the other horses. She needs to trust that she is safe with you, horses that are herd bound aren't just lazy stupid horses - they are horses who lack individual confidence, who need to feel safe. So you need to spend some time doing ground work with her, teaching her that YOU are the leader of your two creature herd. Practice teaching her to yield all parts of her body and respect your space. If every time she sees you, you just jump on her back and make her do stuff she doesn't like, she will see you as a pest, not as a leader. Make yourself her leader.
Also, something needs to be made more appealing about being away from her buddies than being with them. If every time you leave the gate it leads to a horrible fight where she gets kicked and made to work she's going to hate it. So I'd go, get her on a lead and take her out to the gate and let her graze. I'd hand walk her up and down the area you wish to ride while doing things that make her happy. Such as itching a particularly itchy spot, or letting her graze. Do something for her that's more wonderful than just sitting out with the other horses.
Once she stops hating the area so much now make her work. Bring her out on a long lead, walk her interactively (keep her pumped, don't just drag her along). If she stops moving Immediately make her lunge, walk/trot around, then carry on straight. When she's walking confidently and not looking for ways to stop, let her eat some grass or get itchy scratches. Repeat this until she's doing everything you want.
Next I'd practice riding her out and you are right! She Can Not Get Away with that!! Sitting and whacking her clearly isn't working. SO every time she decides to stop moving you should back her up, this will get her feet moving, then while her feet are moving turn her in a circle. Get her walking (better trotting) in circles. Then carry on straight once she's moving. Repeat this until she realizes it's easier to just go straight than have to deal with you fussing at her. I'd also let her stop and do something enjoyable while your out, anything she likes, maybe bring some treats for her while your riding. Don't give her treats when you get home, that just teaches her that going home is even better - you need to make riding nicer. I prefer not to let horses graze while riding, but when they're plugging along nicely and doing what I ask I'll stop them and turn their head to me and slip them a treat.
Good luck :)