Sorry that you are going through so much trouble to clip her nails. The benedryl does cause some sedation in some dogs, in others it does nothing, especially if they are stimulated by something like clipping their nails. There is an oral sedative that your vet can dispense, it is called Ace (Acepromazine). Once you have the Ace this is how you do it:
1- Always do it in the day when your vet is open just in case you need to take her in.
2- Give her the Ace inside of a treat like a little bit of peanut butter. Make certain she has not had a meal at least 3-4 hours prior to giving it to her.
3- After you give it, do not stimulate her. Leave her alone and within 30 mins you will notice that she will be super relax.
4- At that point one person controls her head, ideally with a muzzle and the other clips the nail.
As far as clipping the nail:
1- Do not clip the nail if you don't have quick stop (powder to stop bleeding); can buy at petstore.
2- Cut the nail as close to the quick as possible. If you make the nail bleed do not worry; just use the quick stop directly on the bleeding nail and it will stop. If you have a hard time with the quick stop, use a dry soap bar to press nail against and stop the bleeding.
3- Once the nails are cut leave her alone and observe to make sure she recovers uneventfully; make certain she is breathing ok.
4- To lessen the frequency of nails clipping walk her on concrete.
If you have any questions I will online for another hour.