given the fact that you could not do the planned lesson...and you asked the student if he wanted the other...i would say at least you did not disappoint and send him/her home. most are happy to get flying at any cost and the fact that the purpose of the lesson was a little advanced for the student is neither here nor there....
i am in JAAland but as an examiner i would say that not alone is instrument appreciation a part of the course, but on a flight test i expect a candidate to be able to use any / all equipment in the plane including determining position using vor/dme/adf and vor tracking.
whether the sra was required or simply of benefit is perhaps the question but as you say ..anything that may help to get a student out of a jam is still experience .
has instructor B any reason for his/her complaint...such as you are seen to do things like this that he/she may feel suits your desire to teach such things rather than stick to basics..the fact that you are qualified to teach instrument flying is not the point if such flying does not form part of the course at your school. if it is instructor B should also be teaching it is he/she is suitably qualified...if not and it is on the course then somebody suitably qualified has to do it.if it is not required and therefore not part of your schools course then you should not be teaching it unless your cfi agrees.
over the years at a school i taught at we had something similar...where an instructor was at times SHOWING people how to do an ils and vor/dme as often as he could. now i draw the line there...he was practicing for his own cpl no doubt.ils and vor/dme other than a brief demonstration for the purpose of instrument appreciation is definately not on the ppl course.
as long as what you are doing is part of the course and being taught with the knowledge and approval of your cfi i would have thought that you are in the right.
if you are just suiting yourself then no.
if in doubt ask your cfi.
the dean.