I say go for a trail ride , but ask your friend is she could keep it at a walk , maby a trot here and there. Just this time for your sake. Im sure she wont mind just this one ride.
You don't have to go fast to have a good ride.
We have several stables around here that works on going trailriding with custoers, it's very often people who has never even seen a horse or maybe rode a bit when they were 5. ;)
They as good as always both walk, trot and canter, ride up hills etc and love it. It's very rare that anyone falls off or get hurt.
As long as the horses are bombproof and ''your'' horse listens to yor friend too and don't tend to run off on its own, I'd say go for it! Canter is way easier to sit than trot, and just hold onto the mane if you get insecure.
But it has to be a safe horse and one that isn't likely to keep running if the other stops.
An aren isn't always safer than the trail, I know horses that freaks out because they're just not as used to the arena, but are bombproof at the trail.
But make sure to use a helmet anyways, it's such a cheap life saver :P