Is there anywhere nearby where you can go and just work her in a paddock with cows? The first introduction to cows any of my horses get is trail rides through paddocks containing cows. I ignore them and expect them to do the same.
The next step for me is tagging along when mustering. I let dad do the work on the bike, and I just criss-cross along the back of the mob, geeing up any stragglers. This can be done at a walk on a loose rein, and as you get more confident and your horse gets more relaxed, you can move it up to a trot then a canter. I also practice stops, rollbacks and haunch turns when doing this, keeps my horse’s attention on me and gives them practice performing these moves with cattle nearby. If my horse gets worked up, I drop it back to a walk and back off the cows a little until it settles.
Next thing I do is a bit more hands on mustering; still in an open paddock, but I do more of the work with the bike as a back up. The next step up is moving cows with just weaned calves in the yard, or taking bulls out of the paddock with the cows. Both of these have a bit more motivation to challenge you, so your horse can have its first experience of actually working a single cow, but it’s out in the open in an area where the horse is comfortable. Being in a yard is a much more high pressure situation. Having the bike as a backup is great because if your horse gets worked up they can step in while you settle your horse. It’s now that I start introducing keeping with the cow, (they will have already learnt to follow cows by following the mob) now they learn to focus on the cow and me at the same time. This incorporates stops, rollbacks and haunch turns to keep with the cow, and if needed getting up close and sometimes touching a shoulder to the cow to put a bit more pressure on them. The cows will be a bit more sluggish than bulls (only a bit!) so are a good starting point, but will give you a decent challenge trying to get back to their babies. The bulls are a good challenge for a horse who is getting the hang of working, as they are more aggressive in their movements and also tend to face up to you a bit more than the cows.
Now moving into yard work… I wouldn’t start trying to work cows straight away. I would practice picking out one cow, and moving into the mob at a nice relaxed walk and cutting it from the rest. It will get your horse used to moving through the cattle in a confined space but not put the pressure on it of having to then work in this confined space. Just let her get used to being this close to cows. Once she can calmly go into the mob, select your cow, and cut it from the rest, only then would I start working it by itself. I would start running the cow along the front side of the yard; pushing it across the yard, hanging back a little to let it run, then moving up and blocking it and sending it the other way. I send the cow across the yard and block and turn it maybe 3-4 times before letting it return to the mob and selecting another cow. It stops the cow getting tired or piggy/sticky, lets your horses have a break, and gives it more practice at moving calmly in with the cows cutting out your next cow.