@Jennifer3446 For the medical bill, your friend should initiate a claim on Airbnb's liability insurance. Send him this link: https://www.airbnb.com/insurance/create-claim/liability
If your friend doesn't want to complete the stay, he can give 30 days notice under the normal terms of the cancellation policy and relocate for the final month. Or he can request a booking alteration with the host to advance the checkout to a nearer date. The presence of undisclosed dogs would have been enough to have the whole stay cancelled and fully refunded if your friend had reported it within 72 hours of checking in.
Even if that window has passed, the host should still be reported for not disclosing the dogs. I honestly can't imagine what this host was thinking when they listed a room and took a long-term booking without ever mentioning there were dogs on site, but the fact is that Airbnb doesn't vet hosts or inspect listings. Unpleasant surprises like this are all but inevitable if you book the cheapest listing you can find and it has no prior reviews.