The worst case is that your daughter and her boyfriend will be charged under state and federal child pornography laws. If convicted of possessing and distributing child pornography, they would have to register on sex offender lists and they would have felony records.
HOWEVER, the officer you spoke with is correct. Things will probably be okay.
Prosecutors have discretion and states are after adult child pornographers, not kids who send nude photos of themselves to others. State laws that address child pornography never anticipated kids sending nude photos of themselves to others, and prosecutors are reluctant to charge kids under these laws.
Prosecutors in most states that have faced the problem of kids sending these photos to others have found other means to "punish" the children (and their parents) besides formally charging them under the pornography laws. These punishments have included probation, community service hours, educational classes.
Many kids have been suspended from the schools they attended. Many of the kids in small communities, where stories spread fast, have had problems finding jobs. And, of course, they are humiliated - especially when these "private" photos make their way online (which many do).
You should have an attorney for your daughter, because the possible repercussions she faces with her nude-photo sending are severe. The reality is, however, that the prosecutor probably will not pursue charges against either her or her boyfriend.