Ways to keep my Maine Coon entertained?

I adopted a 4 year old Maine Coon (possibly mix, I don't know, but she looks and acts Maine Coon so I'm calling her that) a few months ago, and she's definitely a high maintenance cat. It took her awhile to stop biting me and to come anywhere near me on her own, and now we're getting along much better, but I can tell she's bored. She's very intelligent and is constantly getting into stuff, and she jumps up and knocks things off the counter and chases my other cat around like crazy because she's trying to play, but he's 15 and not very interested in playing. But unfortunately she doesn't seem interested in actually playing with me. We have wands, strings, balls, mice, scratching posts, those ball on a track toys, etc, but she doesn't do much on her own and isn't interested in playing with me, except very occasionally with the laser pointer (which isn't the best kind of play anyway, but if it's the only way to get her to run around...) so it's hard to tire her out. I've been trying to take her for walks, too, the shelter told me she was already leash trained, but so far she isn't doing well with the harness I've been trying to use so we haven't been able to go outside much since I'm too afraid she'll bolt. Any ideas how I can keep her entertained, or get her to start playing with me? I'd love to adopt another younger cat or a dog even so she could have a younger playmate than my 15 yo, but I can only have 2 pets in almost all the housing I can afford in the city where I go to school, unfortunately. 

You mentioned you have wand toys - do you have the one called Da Bird? I have several wand toys but Da Bird is the only one my cats really like. Most cats go crazy for it, maybe because it uses real bird feathers. You are definitely right that interactive play is key to avoid boredom.

These articles may give you some ideas
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I had a petco toy similar to da bird, but not actual da bird brand, and she couldn't care less about it I just bought a da bird refill online to put on the old toy I had though, so I'll definitely try it when it comes. 

Thanks for the articles!! I've been keeping with the harness training, but she still doesn't like it much. She'll go outside without it (I let her out on our little porch that I can keep her contained on if I'm watching her) but she won't even go near the door if the harness is nearby. She does like playing with the leash as a toy though, she'll chase it like crazy, go figure! (Still hasn't stopped her favorite toy from being the 15 yo cat, though.)

I'm thinking about starting clicker training her though, I'm not sure she's trainable enough, but I've been reading about cat agility and it would be perfect if I could get her to do some agility, even just indoors. All that jumping HAS to tire her out! She's smart enough and energetic enough, but I'm not sure if she might still be too moody to bother learning anything that wasn't her idea. (Her nickname is Moody Maine Coon for good reason, I think she may have had a rough time with one of her past families before I adopted her.) I'm going to give it a try, though.