Hi there,
Congratulations on your new baby. Mine was a "surprise", too, as my daughter rescued her and plop, she landed in our home.
I quickly learned that she had to eat something at least every 2-3 hours. She was not consistent with what she would eat; it rotated between:
nutrical
karo syrup
Bil Jack "Lil Jacks"
Canned food
cottage cheese
dry food (just every one in a while)
Also make sure she drinks water often. I often had to put it in the cup of my hand before I could get her to drink it.
And don't let her play or run around too much until she's eating steadily and has adjusted a bit.
Keep her warm, too.
Oh, and give her lots of love and snuggles!