She is allowed to answer "No" to the record question under the concept of "legal fiction". But, the police generally don't recognize that concept.
Comm2A won a case making a minor MJ conviction a non-disqualifier in MA. Best to disclose the sealed record because of the above but,
even better, get legal counsel who specializes in guns for a consult (Langer, Guida, Tassel before you apply. An office consult should run you about $200. An appeal more like $5k if it involves a court appearance, plus, if you don't get the consult in advance you will be paying your attorney to attempt to correct any strategic missteps on your part.
If she is denied for the MJ charge, let Comm2A know. Comm2a would be more interested in helping a denial for a MJ charge than the very long battle of arguing legal fiction, as the former is settled law in MA. A prominent local business owner in Metrowest was denied for a MJ conviction decades ago. I gave him an attorney's number and told him "talk to this guy, if they continue to F with you Comm2a will take the case". The attorney quickly straightened it out as the PD did not have a problem with the person (who has a great reputation in the community), but thought they were required to deny.
Just remember one thing.... sealed records mean shit on an LTC app.
For MA records, yes. From other states - maybe. Don't know about NH.
In MA, the PD may just get "Sealed record exists is/is not a firearms disqualifier".