What would you do about this?

Can you take a photo of her as she passed? Maybe a couple on different days?

Can you send her a message via the farm thatyou have seen her doing this and that this is putting the lives of horses and people (the order in which people and horses will probably be seen by a stupid woman like this) at risk and that you find it frightening?

Are you on speaking terms with the owners of the stud? If you are, could you express your concern to them? Surely the safety of the horses is of concern to them since it's their livelihood.

On the way to my sons there’s a riding school and the horses sometimes cross the road at some traffic lights. I was sitting in my car as they crossed and some of the riders were on their mobile phones. I should have complained to the stables. As to someone driving a horse box and using their phone whilst driving. That’s totally wrong. Not surprised that the police aren’t interested. Someone I know contacted the police to say he’d seen someone walking near a school carrying a large, dangerous knife ( like a Samuri sword) and they weren’t interested.

@cossy

We cannot catch her doing this on our 'phones as she passes too quickly.

see original script

Have you spoken to the police about it and told them the registration number? That way, if she did (hopefully not) you would have evidence that you’d contacted them about it.

I know anonymous letters are often ignored BUT I think one is warranted in this instance. Send it to the farm pointing out politely that you have seen, or know about, her texting and that it will be reported if it is seen again. You never know you might save someone’s life.

It is against the law to text while driving so the police ought to be interested but if it is difficult to get proof then I think a complaint to the owner of the stud is your only hope. Meanwhile fingers crossed that there isn't an accident.

CountessFosco
It’s been against the law to use a mobile ( with hands) while driving for 22 years.
Hopefully the worst never happens but if she were to crash the horse box and injure the horses you can be assured the insurance company will check her phone.
Then they will be in the right to not pay out as she’s driving illegally.

That you happen to be standing in the lane so that you see her almost always texting on her ‘phone suggests there’s some routine.

It’s the job of the police to find evidence through surveiilance.

This is a similar thing to when someone was letting what must have been a large dog foul a nearby public footpath every day in almost the same place. I reported it to the council. They asked if I could narrow down the time when this was happening so they could have a warden there to watch out for the offender. So I did. The owner was caught and issued with a £100 fixed penalty notice. The fouling stopped.

I used to pass a young woman on the back of a pony with two ponies following on leading reins. She was texting, and the lane was narrow with people frequently speeding and upsetting the livestock. I tried to phone the riding stables but the name had changed and it took me some time to discover the name, number and get an answer. When someone finally answered they were not the slightest bit interested; really, what was it to do with the peasants.
Mind you, I never saw her again.