I think your questions have been answered sufficiently by others (hopefully)
IME there are no guarantees and so breeding a foal to calm down a mare is IMO a risk I wouldn't bother with as there are too many varients out of your control i.e
What if the mare calms down but the foal inherits the temperment traits you want calmed ? Especially if the foal is a stockier version of Mum ?
Do you really think Ruby is breeding stock ?
What if the foal (as crosses of the kind you have described can) does not turn out conformationally the way you want ? Then you have a foal from an unproven mare to care for, pay for, educate and sell (and hopefully find a good home for) ..
If the foal turns out to be exactly, conformationally and temperment-wise what you want then can you care, pay for and educate it properly until it is old enough to make a riding horse (and do you want to ? You are having a few problems with Ruby and - no offence - would you be happy dealing with a boisterous, opinionated, weighty, IDx youngster ?)
I know it's not what you asked in your OP but if I were you, I'd sell the mare (who you haven't seemed to be getting on with terribly well with from the start) and buy yourself a nice, sane IDx which it seems, to me, what you have always hankered for since loosing your lovely Jester.
There is no shame in the realisation that perhaps you are just not ideal for each other - she's a nice mare but I don't think that you two have ever really been that happy with each other.