Hello Brandon…well done for giving this dog a home.
Firstly you really do need to take her to a Vet. Not only to see if she’s microchipped (she may actually belong to a worried owner) but she is obviously not in good health and needs checking over. All new pets should be checked by a Vet within the first 3 days of getting them.
That said she needs worming and a flea treatment, also heart worm meds if they are prevalent in your area. She needs a top quality food, small meals and often. Split her daily allowance between 4 or 5 meals to start with, as she gains fitness and body weight you can gradually knock them down to a meal morning and evening.
Glucosamine is a good bone/joint supplement as is Wild Salmon Oil which will also improve her skin and coat.
I do hope you and take her to the Vet as that is honestly what she needs. If she hasn’t been spayed it would be a good idea to have her done
Good
a vet would really need to take a look at it to truly determine what it is.