Interesting, I thought I'd heard most of the bit terms by now but I've never heard it called a "Spanish D." Seems to be an older term for a Kimberwicke?
I would have to say, "It depends," on whether I would advise using one. My first concern would be whether a ten year old could use one without having the chain constantly activated. When I ride in a Kimberwicke, I keep the chain loose enough that I can ride with light contact and use it as a snaffle, and the only time the chain comes into play is when I shorten the reins considerably.
First I would consider that it is not a bit problem, but that the pony needs more schooling over grids and work on slowing down with this particular rider. Pony might be going, "Yee haw, it's like having no rider at all!"
Second, I would consider that the child has not learned how to properly use her seat and lower legs to give her leverage. A tiny person cannot use their arms alone and stop a strong pony. She needs to learn how to have a strong seat that will not be pulled off balance. She also needs to learn how to use her reins properly and not have them loose until just after the jump and then try to pull up the horse frantically. Or to ride the pony's mouth. And how to brace one rein against a pony's neck and use the other strongly when said pony runs away.
If the child does not have these basics, she should not be jumping in shows yet. IMO.