Hi & welcome to the forum!
First, have you got a trainer or instructor, or very experienced friend who can help? With only a bit of written info, no eyes there to see what's actually going on, can only give general sort of advice here, which may or may not be relevant.
However, she is deeply, deeply stubborn, ... horses, she wants to get back to the barn & her herdmates as soon as possible. So, she'll act up at the start of the ride
Stubborn means the horse has learned to outpersist it's human. So, whether it's you, who have inadvertently 'trained' this by perhaps being inconsistent, ineffective, or previous owners, to teach a horse not to be 'stubborn' means ensuring the 'tantrum' or braciness or whatever, NEVER works for the horse, and what you're asking does work - it is easy, clear and is rewarded instantly.
'Herdbound or barnsour' are a couple of lables for this first behaviour. Yeah, unfortunately common. Means the horse doesn't want to go out with you, be ridden, leave his mates, whatever.
First thing first I think it's important to analyse *why* before working out a solution. Try to address the reason
, change the attitude, not just the behavioural 'symptom'. Eg is the horse new to you, new to going out, not been out much alone? Eg. Is there any fear, lack of trust involved? Or is the horse hurting - saddle fit, back, mouth, etc? So that she's trying to tell you it hurts, until she is resigned to it. Or her previous or current association with going out/being ridden is not pleasant, so she 'tries it on'...
So you can hopefully see there's a lot more to it than just 'correcting'/punishing 'bad' behaviour, and sometimes punishment is not appropriate & will only make matters worse.
At first, her rebellions were pretty mild and easy to handle, but she's gradually increased the severity of her misbehaviors.
What's causing her to get worse? How are you dealing with it?
She had some problems at first, but she had a firm hand and straightened things out quickly.
Sounds like she has learned that this behaviour is working with you, or you're doing something that causes Rosie to 'shout' at you about... & It's working so she will do it more & harder!
before. I grabbed the branch and swung off, but by this point I had been fighting her for a while and she was only getting worse. I didn't feel I could continue productively or safely, so I decided it's best to call it quits and ask for some advice.
Good job I reckon. People will say 'always get straight back on if you're bucked off' and 'never bail/let the horse win' but my feeling is safety first - if you aren't in control, aren't able to be effective, then it's only a matter of time before the excrement hits the turbine and you get hurt.
From a training perspective though, her 'tantrums' are working, so she will get worse & worse. Of course, depends why she's doing it too - pay to check/treat physical probs etc first. But I'd honestly consider whether she really is the horse for you, and if so, I'd really suggest giving her to a good trainer for a time, to evaluate & hopefully get her safer, before you attempt to ride her again
Someone I know immediately suggested a harsher bit (I
Nope. It's not the bit and depending on... Lots, it could just make matters worse. In fact, if she came to me like that, I'd 'restart' her from scratch in a halter first, to ensure she learned to 'follow a feel' from reins without fear of pain from the bit.