It is sad about your wee runt Helen, but you know you've done all you can. Without sounding too twee - this is nature's way of making sure only the strongest survive, you're doing all you can and if it turns out not to be enough (though I keep hoping she'll surprise you like her mammy did
) then it's just part of the circle of life.
When it comes to giving jags we've managed (have to say we, cos I've not jagged my boar - leave that job to hubby, he can jump higher
) to get through it without a crush. My way of doing it - get organised (better with 2 of you) one person stands by with primed needle at the ready while the other puts her food down, as soon as her head hits the trough get that needle in her bum and empty it quick as a flash. She's likely to lift her head and wonder what happened, but should return to eating quite happily. I think it's all in the timing, get her just as she starts eating and she's distracted enough by that, not to notice
As for Aggie's oxytocin - she'll still be kinda phasing in and out at the end of farrowing so you should manage to give it a bit more easily (hopefully) fingers, toes and everything crossed - maybe tonight will be another sleepless one ?
Good luck and give Bonking Boris an extra apple from me