Suggestions with trotting?

Okay so, before I got Duchess I had just started getting comfortable with trotting. I had not trotted for about 1- 1 1/2 months before getting Duchess and now I'm all uncomfortable and nervous with it. I try to force myself to relax and breath and sit deep in the saddle and sometimes it works lol sometimes not so much.
Duchess has a pretty nutty trot right now. She's never had to collect herself or do anything in a disciplined manner so when you ask her to trot, she speed trots and then slows but picks it back up and then slows or just stops. Its nearly impossible to post to without ending up on her neck mid-post when she decides to just randomly stop.
We've worked her on the lunge line twice and the first time was..interesting but the second time I think she was kinda starting to get the hang of it? I can't trot her on the lunge line all the time though because my instructor has her own horses to work and half the time I'm out when she's still at work.

My instructor suggested trying to trot her in a circle to ensure that she can't speed up too much and I can still stay comfortable. Well, the first time I tried it she turned so hard she nearly tripped over herself, the second time I tried it I couldn't get her head to turn for anything O.o.

I can't trot her in the round pen because she's just too big to comfortably trot, she ends up going in a 2ft circle.

I KNOW I need work personally on trotting, my position and confidence (trotting has always been my arch enemy). I can't ride my lesson horse because she's completely lame and John is still green and in training.

Today I'm going to try something new. Since she's too big to trot in the round pen, I'm going to try trotting her around the round pen. It should help me actually keep some sort of shape and hopefully help her understand better what I'm asking.

So far, all we've been doing for the past 2 weeks is just walking. Working on circles/turns and suppling her neck and building muscle. She's done her testing and, for the most part, I think she's over it with the walk. She's REALLY started relaxing at the walk, stretches her neck out and has realized she doesnt need to crank her neck up to my face and race around like a bandit.

Trotting is a whole other story. When you ask her to trot, her neck immediately jacks up and she starts racing. I know with time she will relax in this gait too I just need to figure out a way for me to relax which will help her to relax.

Sorry for the book. LOL.

Any ideas?

I notice in your side bar you say she doesn't have her own saddle yet....???? Has someone checked to make sure the one your using fits her?

How old is she?

The one she's using is a medium-wide. It fits Maroni and they're basically built the same in the withers and back area.

She's 13.

How does she do with lunging? Can you have someone lunge her while you ride?

I think she said her trainer is doing that once in awhile, but can't spend more time with her than she is.

When they go hollow and speed up it's often due to pain. It sure would't hurt to have her looked at by a vet or chiro and see if her body is alignment.

Other than that, I might suggest you ride another horse to build up some confidence in your riding.

I don't have any other horse to ride. The lesson horse is lame.
The vet is coming out in a few weeks to UD her shots/coggins and check her teeth.

We're having issues lunging her because she wont move away. She stays stuck on you and we don't think she's being stubborn they just REALLY drilled into her head not to allow her butt near you. We've tried a number of different ways but until we find something that works, that's kind of out of the books too.

My instructor is going to put us back on the lunge line tomorrow night for our session.

My only suggestion is take her into an arena or some other kind of enclosed area with lots of space. Ask for the trot in a circle and if she speeds up, LIGHTLY tighten the inside rein to make the circle smaller. I don't know what kind of bit you are riding her in but this is easiest in a snaffle. It will take a while because she clearly has never been taught to collect or had specific cues installed for go, stop, turn, slow down, speed up, etc. It seems like they just kinda rode her a lot but didn't teach her much. If she tends to stop when you try to post, can you sit her trot out and work on it that way?

Another thing that works for getting a horse to move "with their brakes on" is to ask for the jog, then if they pick up too fast or start to speed up, stop them and back a couple of steps. Then continue on and repeat, and repeat, and repeat, etc. Do this consistently every time you ride. If you are riding a trail, do it the entire way about 1/2 or 1/4 mile from home. You can also incorporate this into your circles. Even after she starts to really carry herself relaxed, smooth, and slow, continue it every now and then just to keep that gait and after a while, it will be a permanent gait. This method is how I got that wonderful little jog on Dobe.

Just remember that whatever you do, it will not be an overnight fix and could take weeks or months of working every day before she gets consistent but just don't give up. It does work.