When you say "harlequin" do you mean the perfect one with the symetrical mask? Because, the thing is, you find incredible Harlequins when you google it. In real life, Harlequins with the textbook marking are incredibly rare. I've yet to see one outside of an expo... In France, "Japanese" is the breed you find the most in petshops and they look nothing like the pictures you see on the Internet.
Moreover, I would be very cautious about buying an animal via Internet and having it shipped - a breeder who accept to sell an animal to someone they've never seen and to ship a rabbit even though they are incredibly fragile (they can have a heart attack, or die from the heat if they are in the truck for too long and that the weather is too hot, or not eat during the travel due to stress and thus develop GI stasis) is not a breeder I would want a rabbit from. I'm talking mange and your daughter finding a dead baby rabbit in the cage after a few days, here. It happens. Quite often. That might be a concern that outweighs the color of the rabbit - try looking up photos from local rabbits with your daughter, she might fall in love with one who looks nothing like an Harlequin.
I'm sure you've done your research about rabbits. It's great that your daughter is very patient and cautious about rabbits. I feel nevertheless that I've got to give a few words of caution :
-rabbits need at least 5-6 hours outside of their cage or they will go mad and scratch and shake the bars of their cage and possibly become aggressive. They will eat EVERYTHING you haven't rabbit proofed (books, furniture, clothes, shoes, electrical cords... everything - they go into very small space and they jump very high).
-rabbits need to be spayed / neutered. Not doing it is not an option or your daughter will see her pet die from cancer. Also, intact rabbit often spray urine. And bite. And scratch. And scare children (my son / daughter is scared of our rabbit so I'm giving him/her away is an explanation I often see when people rehome rabbits). The operation costs around 150$
- I'm actually against keeping a single rabbit. They are social creatures and need to communicate with their kin. A male / female both desexed couple is ideal. The house rabbit society has tons of good articles on the subject.
- Rabbits don't like to be carried around. A lot of them don't even like to be petted. Taking one in, you might need to explain to your daughter that she can't touch her pet because the rabbit will run away (or growl, or bite) everytime she will try to get close to them. It's not always the case, but it's a very real possibility. I've never met a rabbit who liked to cuddle. The fact that a baby rabbit let himself be petted doesn't mean he still will when he becomes an adult.
-Rabbits have a life expectancy that has been increasing for the past few years. It's likely a 12 years commitment. Will your daughter still be interested in cleaning the litterbox when she'll be 13 or 14?
- Rabbits are easily ill. Vet bills can pile up very fast.
- You'll need space in your house and fridge for the rabbit (a rabbit needs fresh vegetables everyday). Also, there will be hay and fur all over your house.
If you and your fiancée are aware of all that, it's great. I love rabbits, but those reasons are why a lot of serious breeders refuse to sell them to people who've got a child younger than 7. Even the nicest of children can get frustrated with an animal that refuses to be touched and interacts very little with them. I personally think guinea pigs are a lot more suited to children, as they are a lot calmer, less skittish and fragile.
It's your choice, but make sure to discuss this with your daughter so that she isn't disappointed with her pet. Rabbits look like cuddly plushies but they really aren't - I still have a scar from my wrist to my elbow from a rabbit I had to grab to put in his pet carrier. He was the nicest of rabbits but really didn't like being handled at all. I've had this scar for five years now and it will probably never fade. I've also been bitten a few times and all my rabbits are nice desexed free-ranged rabbits.
This article seems pretty relevant to me:
http://rabbit.org/faq-children-and-rabbits/