Give her a bath using whatever dog shampoo you like, shampoo especially her tummy and entire underside, legs, feet, but, etc. Rinse well, blow her dry, being sure her underside including her "armpits" are quite dry. I bet she'll smell like a rose and be much happier, and you too!

(My dog loves to lay on his back spread eagle when I blow him dry.)

If you cannot wash her yourself, then take her to a groomer.

Not sure about the food. I wonder why they didn't feed her regular food. Maybe their own dog eats Purina? She could have rolled or laid in something icky at their house. Dogs love to do that.

Actually this could be a yeast infection.....have the vet test the area

Yes to what Mazer said.

I agree-yeast infection. Time to see the vet.