The 809 takes an 18mm band.
I'm preparing to give one to my father as a gift. I'll put it on a grey nato which I think will go nicely with the matte finish case. I'll also give him a few additional colored natos so he can switch around according to his mood. If you decide to do the same for your niece she can always have a reserve strap and throw one in with the laundry. A rubber strap also sounds good though.

 

18mm Natos are an excellent choice for this model IMHO..

 

I'm really leaning toward rubber so she can disinfect it. Thanks for the band size, that gives me a starting point to search.

 

I would suggest this.

Amazon.com: 18mm MODENA Flat Italian Rubber Watch Band w/ Deployant / Deployment Buckle / Clasp: Watches

Ive had two of these, worn them on 3 different watches, and love them. I also think she would appreciate the clasp on the watch, as it makes it feel a bit more solid IMHO.

 

Thanks for the recommendation mike. Is yours a link collector as some of the reviewers pointed out?

Too bad I cannot find a Maratac Silicone Rubber Strap in 18mm, those look nice as well.

 

I would have recommended the maratac elite composites, but they're actually rather long and won't fit wrists that are smaller than 7 inches. if you do decide to give those a try, you might have to use a soldering iron to melt extra holes to accommodate for the smaller wrists. When they do fit, they're really comfortable despite being synthetic. I'm not sure if they make them in 18 mm, but you could buy a 20 mm and cut a millimeter notch out from each side, then use a soldering iron to seal/cauterize the cuts.

 

My first one attracted some lint, but the second has been lint free. I can not recommend it strongly enough.

 

Thanks for the excellent recommendation G-Junkie, but I'm not the most dexterous person on the earth and would likely screw the thing up with a soldering iron

I'm gonna pull the trigger on mike's recommendation, then I'm done with this watch, she has a good start for her first automatic.

Thanks to everyone for your help, I appreciate it.