Personally, I would report the dog bite to the police...Even at this late date, she should supply a medical report and pictures if she has them to protect herself and others in the future.
RED FLAG! Owners who pursue so much secrecy, often have let other bites go unreported... And anyone who needs an animal so much that they cover up something like this. Well, she needs a less dangerous pet.
Nipping, I could let go, but a bite requiring an ER trip and stitches, no way.
Disclaimer...My sister's ex's-wife's chow attacked and bit my 4 yold niece, whom he knew and loved. He bit her on the shoulder/back, then bit onto her thigh and drug her around the yard...While both adults tried to stop him. Awful, awful, awful. Oh, yes ex and his wife did not want to report their little darling.