Good job trying to do this at home! I also trim and groom my own dogs. I also don't take my furbabies to the groomers. Though, vet techs are probably the best bet if you do take them in somewhere.
Anyhow, I did a lot of reading to figure out the best way to do it at home. It was a slow and tedious process, but it worked for me. It may be a test of your patience... And for you, it may be even a slower process as yours is 4 years old, but nonetheless, I truly believe she can still be conditioned!
Basically, you start conditioning on a daily basis, multiple times a day, and get her to become comfortable with the nail trimmer (I'm assuming you know how to trim and they usually don't bleed).
To do this, do the "touch and treat". I started by holding the trimmer and touching the paws for a split second and giving the pup a treat. Do this several times and then training session is over. After doing this over a few days, transition to touching the nails with the trimmer, again for a split second. Then, touch the nails longer - couple seconds / over each nail / on each paw. Then, actually hold the nail trimmer over the nail, as in to trim, but you don't actually trim down.
All those steps, transition slowly, over couple to several days, and do it multiple times a day, each time giving her a treat for being a good, calm, quiet, still girl. If you find she's still struggling, revert back to the previous step because it means you moved too quickly. I know it may sound like too much time and effort. But it works.
When she can comfortably let you hold each paw and hold the nail clipper over her nail, you can try to clip a nail and give her treats like crazy. And so on.
Hope it makes sense. Just take it slow. I read that you shouldn't have to hold them down or force them (something I also used to do as well with my previous dog). When they're comfortable with it, it's safer and easier for everyone! If you have the will, this is a good way
