you sure are correct about the actual costs of firearm ownership. you can spend 1000 dollars on a 9mm and 500 on 45 cal but after a couple years the 9mm still comes out to be the cheaper option in the long run.
as for grips you can't change them on most polymer framed handguns with the XDM included however there are non skid patches(adhesive backed sand paper) that is designed to fit inside the ridges of the XDMs grips that I believe may come in hot pink. other options are Cerakoting which is a ceramic based paint that is baked onto your gun at low temperatures and from what I've found is pretty durable. you can also try camo dipping from places such as this
where you can actually have patterns like pink camouflage but from what I understand wears off over time. it all depends on your budget and which one she likes the best.