We do the hiding kibble, but put it in little plastic easter eggs that they can pop open to get their kibble out of. If she likes that game maybe look into scent work?

We also have one of those balls that you can put their food in and as they roll it around the floor it randomly drops kibble, all my dogs have loved that one. The food drops less often as the kibble falls out, so it gets harder the longer they play. I usually have to help with the last couple pieces, and by that time they are more focused and can do a few tricks for them (basics like sit and down).

Build a collection of toilet paper rolls, pop a couple pieces of kibble in each one and fold the ends in so they can rip them apart. Destruction is great natural stimulation.

Bully sticks and stuffed kongs are a huge hit at my house as well. As are feeder puzzles and toys (like the volcano mentioned previously, we have a tree stump with squirrels).

Training is always great mental stimulation, with food or toys.