When I'm saying this I am NOT telling you how irresponsible your friend is, just to be aware. This is just what I think: If your friends mother isn't willing to get a farrier, she shouldn't have a horse. But, whats done is done, and lets not dwell on that.
Your friend needs to save up some money, and get the farrier out herself. Tell her to do chores around the house to save up.
Also she should explain to her mum why horses need their feet doing regularly. (Some suggestions: Possibly unridable in the long run, costly vet and farrier fees.... More costly than just getting the farrier out every 6-8 weeks, horse in pain, cruelty to the horse).
In the mean time, your friend should walk her horse on the roads, to wear his/her feet down. But this is only if the horse isn't lame.
If the horse has actually gone lame, tell her to get the vet/farrier or both out immediately. They will treat the horse, if it really needs it, and your friend could possibly give them the money bit by bit, rather than having to save up for ages, as the horses hooves get worse.