Oh ho! I just ran a search for "flirt pole" on youtube and that is fantastic! And so easy to make! What a great idea!
Well, I would recommend that you hire someone to come in during the day and help exercise your dog. Maybe you could hire a high school student (someone with dog experience) or someone else to come in after school and play with the dog for, say, 30-45 minutes a day? (Keeping her there in your yard if she can't be trusted on leash with another walker.) If you belong to a church or other such organization, they might know of some adult suffering from a job loss or otherwise who might welcome the opportunity.
While it gets expensive, this might be a better option than having to spend half your day just keeping the dog active/amused.
If there is another family with an active dog nearby, perhaps you could get the dogs together for a romp session and split the bill. I know you said she isn't good with other dogs, but perhaps if she got adjusted to that ONE other dog, you could exercise them together and then split the costs with the other family.
Can she run after a bicycle (or be trained to do so)? That might also help to exhaust her a bit more, rather than just going for a typical walk.