That dog is bored and misses their mom... I know it sounds stupid but try to put yourself into the dogs... shoes? Paws? Dogs have a daily routine, if your friend is fine enough to have a phone call, ask her about it... if she's too sick, make one yourself. Go for walks, alot of walks, long walks. Let the dog sniff around for stimulation. You can very easily DIY some fidget toys with treats and old towels or a dollar tree blanket or depending on the size of the dog, empty toilet paper rolls even.

Make sure to tell your friend to never ask you for this favor ever again though.... some people are not empathetic enough for pets... not ment to attack you, my best friend literally hates all animals unless they're on a plate, she got other qualities 🤷‍♀️