I've applied to both MPP and PhD programs, so I can speak from experience. I would encourage her to tell her professors that she is applying to both and ask that they make two drafts of the letter. Truly, most professors would be able to make the change to just one or two sentences, and they shouldn't mind. It requires a bit more organization on her part and theirs, but it makes the letters feel less cold when programs receive them. I ended up creating a shared spreadsheet with application deadlines, program type, and the professors from whom I anticipated receiving a letter. This kept everyone on the same page and allowed me to avoid generic letters.