Deterrence is certainly in the national interest, but you do have a point about whether the kinds of exceptionally long sentences the US courts love to hand out are more effective than more moderate ones as is typical of most other industrialized democracies, which also tend to have a greater focus on rehabilitation rather than retribution, and sometimes better law enforcement. But Holmes definitely deserves to be put away for years because of the severity and betrayal of trust inherent in this fraud.
She wasn’t “penalized” for the right to a trial. She was presumably offered a light penalty in order to secure a conviction and avoid the time and resources inherent in a trial. Why would anyone ever accept a plea bargain if the offered penalty is the same as what they’d get if they were found guilty at trial?