hayduke, you can either modify the seat or get a aftermarket seat, many have them, you can check on the xt225.com site. I think the seat can be cut by down two inches easily and be comfortable enough.
There really isn’t anything else out there I looked, the XT225 is already the lowest bike in that category. In time she’ll get used to not flat footing it, until then if the seat isn’t enough maybe she can get some boots with a thicker sole.
I wear the Frey Daytona lady star boots
to ride my street bikes because I’m 5’5”. With the boots and insoles I'm 5'6.5" and I have shaved/modifyed the seats on my street bikes, one is lowered and I’m still on the balls of my feet. I’m almost flatfooting the XT with my regular off road boots and I think once the suspension gets broken in I’ll probably flat foot the bike.
Good luck and I hope she gets the XT