Well,
I guess you on the 7th of October can reserve seats in the same car for the next day's ride;
when you hope to secure adjacent seats in advance,
presumably the best procedure is like the following.
(1) You and your friend each
purchase Hokuriku Arch Pass online
and print out the exchange order sent via e-mail.
(2) You reserve Shinkansen train seats for you and your friend,
using your credit card,
through the JR East reservation website
(by 23:40 of 2018/10/05 Japan Standard Time);
you write down the reservation number
and print out the confirmation screen or e-mail.
https://www.eki-net.com/top/train_reservation/english/faq/faq.html(3) On the 6th of October:
You arrive at Narita Airport,
bringing the two printed matters and the credit card;
you receive your rail pass and head to Tokyo.
Your friend arrives at Haneda Airport,
bringing the printed exchange order;
if JR East Travel Service Center (Haneda) is still open,
she receives there her rail pass.
(4) On the 7th of October, in the morning:
You and she together
visit the nearest JR East office
among those listed on the Hokuriku Arch Pass website.
http://hokuriku-arch-pass.com/en/location.htmlShe receives her rail pass if she has not yet.
You tell the reservation number to the staff.
You and she each collect the Shinkansen seat tickets,
showing Hokuriku Arch Pass.
Note
: When you make the seat reservation through the website,
you specify the ticket window where the tickets should be collected.
: If her arrival is expected in the evening or the night,
she may not receive her rail pass at Travel Service Center (Haneda),
because this office is open only until 18:30.
: In NRT Terminal 1 or 2,
you can receive your rail pass until around 21:35
(i.e. just before the departure of the last Narita Express train);
after the business hours of Travel Service Center,
you can visit the nearby JR Ticket Office, which is open until 21:45.
https://www.jreast.co.jp/e/customer_support/service_center.html: In Tokyo Station or Shinagawa Station,
you or she may not receive Hokuriku Arch Pass or collect the tickets
at a ticket window managed by JR Central,
who is not the issuer of this rail pass.