Ears do bleed a lot so don't worry that is common.
If you have any of the Kwik Stop or other powders used to stop a bleeding toe nail or if you have a styptic pencil for shaving cuts you can scrape off some of that and you can use either of those to stop the bleeding on the ear.
You can also see if holding an ice cube against the ear (in a plastic bag) above the cut by a little bit and over it will stop the bleeding by slowing blood flow.
You can also use some corn starch or flour in a pinch as a clotting agent to help stop the bleeding.
If your dog keeps starting the bleeding up again by shaking the head you can tape her two ears over the top of her head so they can't flap when she shakes them. Paper tape or vet wrap might be the best choice for that.
You can also use an old sock (depending on the dog's head size and the sock) and cut the toe out to slide the whole thing over her head like a snood to hold the ears against her neck to keep from reinjuring it. You can see a dog with a snood holding its ears down here for an example
Depending on how big the cut is you may want to consider seeing the vet about antiibiotics. If its just a little nick you may be able to treat your self by cleaning the area with betadine iodine solution and Neosporin or Triple Antibiotic ointment once you get the bleeding stopped.
If its a big slash then seeing a vet to see if it can be stitched might be a good choice.
This site may help you locate an emergency vet if you thing youneed one
Hope this helps you!