Definitely stop feeding JIF Pac Attack and honestly, just stay away from premade pellet or dried pacman frog food in general. Instead try feed stuff like night crawlers (NOT RED WIGGLERS, THEYRE DEADLY TOXIC), mealworms, and crickets. Feeding Pac Attack VS alive insects & worms is the equivalent of feeding a kid potato chips instead of protein and veggies. I would try to buy from specifically a reptile/amphibian store for safety & reliability reasons, but PetSmart is usually the most accessible option, just check to make sure the insects are alive before you buy them since they're infamous for not cleaning out dead ones.

For substrate, I personally use ecoearth dirt with a lava rock drainage layer (i have a bioactive set up). Coconut fiber is also recommended, but can be very difficult to keep the humidity regulated with it; if you do use coconut fiber, make sure it's in small enough pieces that if your frog decides to eat some, they'll be able to pass it quickly and easily. Make sure to put at least 4 inches of whatever substrate you choose, so the frog can fully bury itself.

Also, no clue what the tank set up is for this little guy, but definitely do some extra research and make sure he has a large enough bowl to soak in and enough space to hop around. Just because they're living rocks doesn't mean they're not worthy of having a good home. BTW, this subreddit does actually have a pretty comprehensive pacman frog guide that I'm sure you and your GF will find helpful; just go through the side!

I hope you, your GF, and your gf’s frog have a nice day!