Can't necessarily disagree with my friend Dr. Milkmaid; with some caveats.
Pelvic bone sutures on most British/Continental heifers fuse at about 27 months... if you can get a calf pushed through the birth canal before those sutures fuse, there's a little bit more 'wiggle room' than if those sutures are fused/ossified... and it seems that things 'spread out' a bit, and never go back to the way they were before... so, if at all possible, I prefer a heifer deliver on her own, or have it delivered by forced extraction - pulling - but sometimes that's not in the best interest of the heifer or the calf.
Every case must be evaluated on its own merits.
If it's an issue of a too big calf... keeping the heifer and breeding her to a calving ease bull the next time (or times) out... may be greeted with success. Or not.
Had a group of wild-@ss SimAngus heifers about 10 years ago that didn't breed up well - and most left as open 2-yr olds... but one... had a really hard pull to get the first calf out(calving ease bull)... damaged the calf, and something about her pelvis just didn't feel right... prominent 'bump' on the floor of the pelvis, and in retrospect, probably too narrow. Didn't get her sold... and the next year... dystocia again, necessitating a C-section. I didn't keep her around for a third try.