I would hold off on changing pegs for the pillion until she rides for a while and figures out what's comfortable for her. She'll need a couple rides that last for a few hours, for her to really settle in and decide what's actually going to be a long-term discomfort, as opposed to just a temporary discomfort as she gets used to being a passenger. If she's a novice who hasn't been in the saddle for more than a short ride, being on a bike for a four or five hours is probably going to be uncomfortable at first, no matter what adjustments you make. My girlfriend can be on the bike all day, as long as there hasn't been a long time span between rides, but if she doesn't ride for a while, even a two hour ride can be uncomfortable.
There are a myriad of aftermarket seats to try; some will tell you that a Corbin is perfect, others will say Corbins are too hard and a Sargeant is the way to go. One seat that's pretty universally acclaimed is a Russell Day Long, but they're one of the more pricey options. My girlfriend was no fan of the OEM seat on my old 2012 DL650, but she's fine with the OEM seat on my Super Tenere. A seat that's comfortable for you both over a long day is probably the wisest investment you can make. I still use the OEM seat too, though I've put an Airhawk seat pad on mine. That's good for me for about eight or ten hours in the saddle, which is about as much as I want to ride in a day.
On my V-Strom, I had my OEM rear shock resprung with a heavier spring by Cogent Dynamics. It made for a better ride when I was riding two-up with a load of gear. On my S10 I had a stock rear shock rebuilt by Norwest Suspension with new valving and an 1100 lb spring. Both modifications made for a better ride as far as having a passenger and gear for two is concerned. I've never made any modifications to the front suspension on either bike.
A backrest is pretty important for a passenger. I have a small Pelican knockoff as a top case, and my passenger backrest is simply a $20.00 ATV seat pad from Walmart, folded in half with some egg crate foam stuffed inside. This pad is attached to the forward part of the topcase by a couple of quick release nylon straps. My girlfriend says it's very comfortable.
One thing I did was install a power outlet that was accessible to the rear passenger, so she can plug in her phone, or recharge her comm unit while we're riding. On my Super Tenere, it's a Motopower USB outlet that's attached to one of the passenger grab rails.
"No matter where you go, there you are."