I have a 5-6 month energetic rescue. We end up walking 4+ miles per day, broken up. I get that you can't do that but also it isn't really enough. I prioritize a play date every day. I schedule it, "borrow" friends dogs, or take him to a dog park. This is the only thing that really works (and makes him so happy!).

In your case, if doggy day care doesn't work, I'd try to get a dog walker midday. Ideally with some dog interaction.

I follow a reddit forum, puppy 101 and they have lots of ideas on enrichment and tiring dogs out besides walking. A lot already mentioned (kong, puzzles).

Mine is 7 months and my schedule allows one short (25 min), and one longer walk -- 45 minutes a day (it's a 2-mile walk with tons of sniffing), didn't think she was still too young for that.

I have an older dog who plays in the yard with her, it really helps.

All that said, I'd suggest r/puppy101 for more ideas, sounds like wearing out your pup's mind is key. I hear you on being busy - the daycare idea is great even once a week.

Do you have a back yard? If not, how about a Sniffspot if she’s too young for a dog park?