I'm another one with lots of crowns.
These can be done in several ways, in one the tooth core can be kept intact, the tooth cut to a stump and the crown fitted as a sheath over the stump. In the second method, if the nerve is too close when cut away, then the tooth can have the nerve removed, the root then filled and then the crown fitted. In the thirs method, if there is not enough tooth left to stick a crown on, the dentist can remove the nerve and cement a metal post into the root, onto which the crown can be attached.
Generally they don't hurt once the tooth has settled down from the treatment, unless the crown is placed ina position where it is fouling another tooth, which is why getting the bite right after fitting one, is important. If it is fouling another tooth, it will hurt and the dentist may need to make some adjustments so that it doesn't.
if it continues to pain her she should see the dentist again. Sometimes the nerve can flare up, even if it was removed as sometimes there can be bits left in obscure roots or it can even abcess.
Hope she gets it sorted as it can be very miserable to be in continuous tooth pain!