I'm not sure whether it's "stick with the legal schedule no matter what" or acknowledging that she's a teen beginning to have her own life.  But, I'm not crazy about a 15-yo dictating what a family of 5 other people should do that disrupts their holiday plans.

I would say if she wants to come to your house on Thanksgiving and it's a 3 hour drive then it needs to be on your terms. For example if you are having a big dinner on one day then explain to her she'd need to come the day before, at least and be driven home the day after (or whatever works for you based on what she has going on.) If she tries to argue and change your plans then don't agree. Just say that doesn't work.

Don't allow her to dictate. Not with such a long distance involved and on a holiday. 

Absolutely stick the the schedule.  To the point that if BM fails to surrender the SKid per the COd schedule your SO smacks BM with a contempt motion. Every time.  Kids being minors, do not get to choose so the violation of the CO is on the parent failing to surrender the child.  In my legal layman's opinion that is.

Have the SKid see the violating mommy or daddy get their skivvies in a twist over having to respond to a court motion each and every time the SKid does not arrive as scheduled.  Every..... single...... time.

If the SKid just shows for gifts, make sure they get a card with nothing but a curt, short holiday or celebration message in it and tell them that since they are making the relationship transactional that they will earn gifts by absolute compliance with the visitation schedule. No visits, no gifts.  Have a stack of bundled cash on the table and point out that had they maintained the visitation schedule with a positive pleasant demeanor for the entire duration of the CO up to that point, that would have been their gift.

KISS

As for BM dumping and running on their own COd SKid time.  Make sure the court knows about that too. Though in our case the moron in the idiot bottom 10%er of the legal profession family law judge in the Harry Potter robes slinging the wooden Fisher-Price toddler's hammer could give a flying rat's shit about the violating parent dumping the kid on anyone and everyone they could victimize with their idiocy by dumping the kid.  For 16+ years of visitation our kid saw his Spermidiot only a few hours per visit.  Summer visit was 5wks and rarely did SS see his "dad" more than a few hours over the entire visit. If they bothered to take the visit at all.  When SS was a toddler, the SpermGreatGrandParents on both sides were his primary caretakers and interface during a visit.  After the SGGPs kicked the bucket then it was the SGPs and primarily only SpermGrandHag that had any interface with SS while on visitation.  SpermGrandPa was not a fan of my SKid and was far more interested in Spermidiot spawn #2 who is the only female loin product of the Spermidiot. That probably should not be surprising as SpermGrandPa dotes on his daughter and the Spermidiot has always been an embarrassment to his own father.  SS being the male product of a detested male child and SpermGrandMa paying SS's CS and paying for all of the visitation travel pissed SpermGrandPa off to no end.  He took it out on my kid.

Anyway, when we became aware that SS was not seeing his "father" during visitation we petitioned the court to end all visitation or order that visitation was actually spent with the Spermidiot.  The robed moron yawned and told us that the "respondent" could dump the kid on anyone he wanted to and did not have to see the kid at all. His time, he could dispose of as he wished.

Over the 16+ years SS and DW  (and me) lived under a CO there were a number of periods of a year or more when all visitation was refused. There was also a period of 2yrs when the Spermidiot moved to the opposite coast without informing my DW and SS flew to SpermLand for visitation when his SpermDad was 3000 miles away.  Over the course the CO years we have no idea how many years that SS did not lay an eye on the SpermIdiot or hear his gangbanger wannabe voice.

One of my vindictive SParent fantasies has been to go to law school for a JD when I retire then to be a pro bono PITA attorney supporting quality side BioParents and blended families in exsanguinating the toxic side with overwhelming displays of the facts and putting their bared  toxic asses on display.  Unfortunately I don't have the vulgar levels of wealth it would take to have the most fun with it.

A 15 year old does not dicate orders to parents. Here is your opportunity to turn the table. She wants to come for Thanksgiving? Then you and your DH discuss, pick the day that works best for him to pick her up and give said date to CHILD. If it doesn't work, then she misses Thanksgiving with you. I'd also have a firm RETURN DATE so she is clearly aware. Want to leave early? BM needs to come get you.

You and your DH have all the power here....please use it and get the 15 year old straight on how you will handle visits from here out. If not, you'll be dealing with this for decades. 

That's why i'm "Team CO". If you insist it's folllowed from the start, then if they want to make little changes during the teenage years, it's not as bad. But in this case, the CO was thrown out the window years ago. It becomes to the point that SD and/or BM are calling the shots, tossing the poor bastard crumbs of time at their convenience and if he doesn't just say "yes ma'am", he doesn't see skids at all. Kind of like Rocky Roads situation. That sucks for the bioparent who just gets crumbs but sucks even worse for the stepparent. I would take more time with skids with predictability over less time but never knowing when your plans may be disrupted last minute at the whim of BM or SD. Teens are inherently selfish but it's a parent's job to parent that out of them. Do what works for you guys and have DH explain to SD how a 3-hour drive to pick her up affects the plans of DH, OP, and 3 other children. 

Just NO. you are not playing taxi on Thanksgiving day. Not driving 3 + hours traffic each way to have her for a hour.  She makes other arrangements or stays with BM.   Stop it ... stop the crazy train 

This is a game DH will never win.  BM sets up a test for him using SD as a pawn.  If he follows thru , she sends SD all riled up and it's a rotten experience.  DH doesn't play the games and SD gets her head filled with " he doesn't love you, you've been replaced by new kids". Blah blah blah.  
 

The only way to "win" this game is take back control over your life and say yes or no for your own benefit.  Compromises with dysfunction people are not true compromises.  This is why the recommendation to follow the CO is stressed.   " sorry you can't make it this time ,we will miss you,  see you next time" is a great answer to a busy teen.   
 

BM is doing this just to be a PITA and retain control over her ex.  She's like a cat  playing with a dead mouse.