I've been doing our mare's feet for years after are old English farrier convinced me that I could do them myself. I do one mare a week and just use a file, so they each get done every 3 weeks like you are doing. If you do them that often, you shouldn't need nippers. I rarely use a hoof knife, either. Also, like you, I had our farrier check my work the first few times. I've done this for years now and the girls have never had hoof problems. It's a great way to be with and learn about your girl's feet...every horse is different.
What I've learned...
- Hoof rasps are very sharp
Even with gloves, be prepared for a few knicks, torn gloves, and pants.
- Concentrate on the toes. Only one of our mares ever gets long in the heel. Even many farriers take too much off the heel and you wind up with a sore horse for a couple weeks.
- You don't need to be perfect...you're not fitting a shoe on the bottom. Riding will naturally clean them up a lot, especially if you ride a bit on an asphalt road (was our farrier's recommendation).
- Get a new rasp when it starts to get dull. It's a lot more work with a dull one. I replace mine every year.
- It's less work in the winter when their hooves don't grow as much.
- In the summer when it's been hot and dry around here, it is much more work. Their hooves get really tough when they are very dry.
- If you're doing the tops with the foot on your leg/knee, try getting her used to putting it on something (or get a hoof stand). Your back will thank you. I don't have a hoof stand and I've used a tree stump and a truck jack stand and they've done fine.
Good luck...I think it's great that you are doing it yourself.