My opinion is that full disclosure of this potential conflict of interest is necessary in the answer itself.
The question is "would use of Wikimedia images be considered unprofessional"; it is a subjective question, and it is clear that being president of a national Wikimedia branch affects significantly her view on this topic. The fact that she is not paid for this position is irrelevant.
Disclosure of this fact in her profile is not sufficient: first of all it is information that should not be one click away from the answer, and more importantly profiles (unlike answers) can be changed at any time without notice.
Her answer is (unnecessarily) apologetic of Wikimedia images in several passages:
it is possible to find great images in Commons
There are great pictures on Commons.
There are many professionals who use their free time to provide Commons (and hence Wikipedia articles) with illustrative, clear graphics.
It should be made clear that this is not the opinion of an independent academic user, but the one of a person who is significantly involved in the project.
- "Should I always disclose my opinions beforehand?" -- this looks like a straw man from her part.
I have nothing against her, Wikimedia or her answer, and I welcome her contributions to this site, but I think that an user should disclose this kind of information whenever they reference explicitly an organization in which they are actively involved. We have had some cases of advertising of one's own projects on this site, and it is always better to err on the side of transparency.
(full disclosure: I have contributed to Wikipedia by editing a few pages in the past.) :)