I'm not the ''shoulder to cry on type'' i would try to pacify them to a certain degree, but as stated in your post, it was agreed by both on mutual terms, so without sounding heartless '' whats the problem''
Obviously she hasen't come to terms with it yet {only 24 hours since split} or she did'nt want to split up in the 1st place, who decided 1st about a mutual split? if it was her bf, she may well think there is someone else.
Is she out with the girls tonight? if so, i'm not sure she should be going as its to early for her to let her hair down, plus i think it would have an negative effect on the rest of the girls, in her defence, 3 years is quite a time with one person, so there ain't going to be a quick fix solution, once you girls can get a smile back on her face and get her ''back on the tiles'' so to speak, hopefully she will see the bigger picture, theres plenty more fish in the sea, times the great healer, and in this case, its only a relationship {assuming no kids involved} that has ''drifted apart'' shes not the 1st, and by ''no means'' the last that this will happen to.
She will be ok, i'm sure of that