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I second Sandra's comments about what a wonderful and helpful group of
people you are!
I received some very helpful information:
1.  Onset of lactose intolerance can happen at any age, and many
reported that as we age the risk increases as we are likely to
eventually lose the lactase enzyme, regardless of whether or not you
have CD.
2.  One person reported that reactions to gluten can change overtime,
generally to increasing sensitivity.
3.  Many commented that due to ingredient changes, my mother-in-law
might not be truly GF if she is not always checking labels even on her
regular foods.  If that's the case, she could be doing villi damage and
there is now enough damage to prevent her from digesting dairy.
4.  Try the lactose diet and see if she improves was suggested (she is
trying and I haven't spoken to her for a few days so I don't know yet)
5.  One person gave advice about a pulse test to determine sensitivity
to lactose and also had suggestions for staying lactose free in
medications.
6.  Other diagnoses were suggested- collagenous colitis, refractory
sprue.
Thanks again for all your information and support!
Bev