> ... it took some elbow grease and Silvo to get it clean
I'll give my standard warning to anyone reading this that you need to make sure that you're using the right polish for the right plating. As an example, don't use silver polish on nickel-plated keywork. That Jupiter almost definitely has nickel-plated keys. You also want to use non-abrasive, non-tarnishing polish.
> The brass coloured one
There's a brass colored one?
> My completely wild guess is that a 12 year old girl might have a bit of trouble with the volume of air needed to play the Bass C.
Three things. First, Jupiter doesn't make a low C bass. Second, the Selmer looks like a low Eb horn to me. (If I'm wrong, please correct me. I think I counted the tone holes right.) Third, I'm going to pick on you a bit, Flyboy.
I'll first mention that the comment is just off-topic for this thread. It's about choosing one horn or another, not whether the student is capable of playing the instrument. Second, if the student is really committed and has asked the Powers That Be -- which should be parent, teacher, and band director -- if she could play the instrument and has gotten approval, it's a tad insulting for some random person to say that the student isn't/won't be capable of playing the instrument.
Anyhow, answering Elaine's questions ...
* I don't have any experience playing Jupiter instruments. I have played a bunch of Selmer USA (I'm pretty sure it's a Selmer USA horn) and Selmer Paris horns and they're pretty decent quality, so I'd go with the Selmer. Again, I'm noting that I only have one picture of each horn to go by and that's it.
* I'd say that both instruments will at least need to have new pads installed, however it does depend on how well the horn was stored, etc. I can't see any show-stopping damage in either picture. I'll again mention that I only have two small, somewhat out-of-focus, pictures to go by.