Your best bet is to have her DNAed, it's impossible to guess. I got a dog from a California shelter, he looks similar to yours minus the black, but same ears and curly tail. He was listed as Basenji/Chihuahua. I had his DNA tested. Out of the 14 possible contributors in a 3 generation pedigree, they managed to pull out 2 Poms, a Maltese, and a GSP... no Basenji, no Chihuahua. That leaves 10 contributors unaccounted for, he's a quintessential street mix. I'm sure yours is the same, except from the beach!
she was found on a beach & no-one came forward for her
We found a puppy on a beach in Ireland when we were sailing / camping there. My son (then aged about 5) walked for miles carrying the puppy in his arms and telling me 'dogs need exercise'.
When we came to leave, the camp superintendent told us the site was closing next day and the pup had been abandoned weeks earlier, very tiny. So we dropped him back into the car and drove home with him. Like Topsy, he grew and he grew ! Definitely greyhound in there somewhere. A lurcher and a fabulous family friend who brought Paul up !!
He was my first dog since I was tiny myself - so I know beach-found doggies are very special.
Have a DNA test done and then you'll know more about him.