US-UK

Honestly I don't know how far a letter like that will go to persuade much in your favour...and presumably the CO is aware of cultural norms already.  There's nothing inherently wrong with a 15 year age gap, however it is uncommon for the female to be 15 years older in Pakistani culture from an embassy standpoint.
 
Of course, there's no harm in exhausting all avenues at this point. 
 
The age gap was just one of the factors the CO used based on the totality of evidence presented in your case (which was very little, as you know)---it was not the sole reason for denial.  You need to stop focusing on the age gap alone.  You were denied based on the combination of all 8 points outlined in the NOIR---not just the age thing.  When you sent in the rebuttal, you didn't really address those 8 points with evidence, but using mostly/only 3rd party affidavits and your own statements...which was not enough at that point in the process to gain approval for the visa.
 
Much better to reapply at a later date when you have more face-time, more evidence of living in marital union, etc.  It's good that she is consulting a lawyer, now.

No one is judging you, not one single person. Everyone is being truthful and you are being naive, rude and defensive. You are legally married, whether you want to admit it or not. The Catholic church does not do weddings to appease families, they do weddings to marry people. You're married. 
 
This is an immigration site where people come to for advice, you were given truthful answers and you accused people of being "too judgemental and hard on you". If you didn't want truthful answers, you shouldn't have asked a question. Just because you don't like the answers you've been given does not make people judgemental, it makes them truthful.

It might be shocking to you, but people with kids are in no way better or more important that people with no kids. 
 
Uscis does not care about your children. The world doesn't care about your USC children either. You as a parent care for them but you don't get prioritize because of them. 
 
That would be an absolute discrimination against people with no kids and USCIS won't have any of that. The USCIS also doesn't care about your thoughts on immigration. 
 
Instead of this pointless arguing you'd do better spending your time preparing the i130 packet. The sooner you start the sooner the 12 months clock will start going.