I helped someone that also said they couldn't get records because of the fire, turned out she was repeating what she was told by another and hadn't filed a 180. Also turned out her relative was a Marine not Army. So I am going to ask...Did the daughter have his Army service number and file a Form 180 formally requesting records from the NARA? Is she sure he was Army and not Marine or other service as Marine records were stored with Navy records and not stored at the NARA in 1973 and should be available.
Did he have military honors at his funeral? Maybe the funeral home has information. Has she talked to his siblings if any still around?
Contact the local Veteran's orginazations where he lived, he may have been a member at one time. If she knows when he enlisted, when he came home she can read the local paper for news of her father. Might find a mention. Newspapers of the time were more focused on "local folk" than now.
The next best thing to knowing exact Unit is to read the history of the ETO, going by his date of enlistement and discharge she can narrow the units he may have been in and be informed of overall activities.