I have never flown a dog, but I understand that sedating them is not the best way to go. If she is used to her crate, she should be fine. I would take all the dogs for a very long walk together when you first get there, then all go into the house together. Have your MIL take up all special toys or leather chews, any "high value" items. Then just 'expect' peace and you may well have it! Lots of exercise for all the dogs, and showing Shelby how the dog door works a few times and she should have that down pat. I predict that she will want to stay close to you and will not try and escape. I hope you all have a great time!
Anne in Tampa
You will have to have a container for water - even though we all know that she will dump it instantly - it should be something attached to the door. I wouldn't do food.
Nope you do not need to sedate.
If you freeze the water first, it will maybe last longer…
And I concur.... do not sedate
UPDATE! 
Shelby and Travis are successfully in New Mexico. I will be joining them in a few days. The airline was wonderful and handled her with care. Travis was so cute and made "live animal" and arrow stickers for her kennel. He made her kennel his project and did a great job. We purchased attachable feeding cups and got a busy bone for her. She chewed up the attached cups in the car 
but other than that it was a non event. I guess she was a bit grumpy when he picked her up though, but I guess that's to be expected.
We did get her micro chipped AND that night the chip was sticking out of her fur! So we had to go back and have the vet do it again. Speaking of vet, they were VERY passive aggressive with me. They know me and Shelby well so I was surprised. She is not fixed yet. The gave me a horrible attitude about that. They snottily asked me how they were going to micro chip her since she wasn't sedated "getting fixed". Grrrr. I was so mad. They also acted like I was going to ship her off to sell her. Kept asking me her final destination and wanted the address. I am still fuming about it and thinking of switching vets. I would have appreciated them voicing their concerns rather than giving me such attitude. When I turned away they kept whispering and….grr...can you tell I'm still mad??
Anyway...everything went well and I'm hoping it is an equally good experience on the way home!
Never heard of being sedated before microchip?… Granted the needle is "huge"... considering.. but I just help a friend chip Silky puppies (8wks old) and certainly they were not sedated (the pups do "scream" but only for a second or two)? And what is it their business if you were shipping her someplace?... I am pretty sure I would be looking for a new vet....
Of course unless you are showing her, best that she would be spayed...
It is common practice at many vets to microchip during the spay/neuter. I think this is in part because many people just never "get around to it" and in part because they have many client animals that are not that easy to handle when using such a large needle.
I have my puppies done before they go to their new homes. Usually at 8 weeks when they go in for their first set of puppy shots. I have never been given a hard time about it though the majority of microchip implants they do are done during spay/neuter procedures. I do also have to remind them when my animals do go in for their spay/neuter that they are already microchipped.
It is common practice at many vets to microchip during the spay/neuter. I think this is in part because many people just never "get around to it" and in part because they have many client animals that are not that easy to handle when using such a large needle.
I have my puppies done before they go to their new homes. Usually at 8 weeks when they go in for their first set of puppy shots. I have never been given a hard time about it though the majority of microchip implants they do are done during spay/neuter procedures. I do also have to remind them when my animals do go in for their spay/neuter that they are already microchipped.
Certainly understand that.. but still, if you are going to do an 8wk puppy without sedation, certainly an adult is no different… just "bigger"... and certainly can understand using a muzzle to get it done... IMO, harder to hold an 8wk old then a full grown adult...
We will not be showing Shelby and I have no interest in her having puppies. She is a mix (shhh don't tell her!! haha), so I don't think it's very responsible. She will be getting fixed shortly after we get back from our trip and I save a few pennies (I'm not paying for this trip BTW b/c taking care of her would have been a bigger priority.) But yes, the vet said they prefer to do it while she is under sedation getting fixed because of the size of the needle. Their attitude about it just sucked. She actually questioned how I expected them to do it??? I was like "ummmm you tell me!!" Shelby has been an angel with all of her shots and she was an angel for this. Yelped a little, but that's all.
Well again… I might be looking for another vet, as they could have just come out and asked you about spaying her...... but then on the other hand.... it is time to get her spayed.... asap... imo.... and you are right would not be responsible to let her have pups.... Good for you to schedule the spay as soon as possible...
I had Nicky microchipped as an adult, Rally as an older puppy and then my others are 8 weeks. Nicky flinched signifcantly when they put his in resulting in it being off to the side. Most of my pups done at 8 weeks also ended up with them slightly to one side or the other. Rally is the only one that is pretty much centered.
I do think that those of us with well behaved dogs take for granted how truly difficult it is to handle a dog that is not used to regular handling. I don't just mean risk of getting bit either, I mean just a young adolescent dog with no self control. Working in the shelter, I see lots of dogs like this, any physical contact puts them over threshold, they wiggle and squirm and if you think a puppy is bad, imagine that same reaction in an 85 pound adult.
That doesn't excuse rude behavior on the part of the vet or their technician but it is the reason many do microchipping during spay/neuter procedures. I would probably start looking for another vet also if their attitude is as bad as it sounds. You need to have a vet that will listen to you and that you can trust.
I would make sure to look for another vet, and I would call the other vet and let them know why you are leaving their practice. Talk to the main vet or office manager and tell them know how they made you feel. Vets are not cheap and if you have a business that service people and their pets you had better be nice, too many vets that are cordial.
