I have had no reason to remove DRM from Kindle books. However it is unlikely that anything would remain to impede your Mom after conversion to ePub for iBooks. The stripped MOBI file won't load in iBooks without conversion.
I have stripped my old Sony library (ePubs from Sony and other ePub vendors to use on my iPad and Kindle. Both devices handle them fine.
Of course, it goes without saying that doing what you propose is likely to be illegal in your country, and definitely against the T&Cs you accepted to buy the Kindle titles in the first place.
amjb
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