Learn English – Expression for someone who is not a professional, but still an expert

A term that has laudatory connotations is language maven. Wikipedia defines maven as follows:

A maven (also mavin) is a trusted expert in a particular field, who seeks to pass knowledge on to others. The word maven comes from Hebrew, meaning "one who understands", based on an accumulation of knowledge.

As Wikipedia further notes:

Since the 1980s it (maven) has become more common since William Safire adopted it to describe himself as "the language maven". The word is mainly confined to American English, but did not appear with the publication of the 1976 edition of Webster's Third New International Dictionary; it is, however, included in the Oxford English Dictionary second edition (1989) and the American Heritage Dictionary fourth edition (2000). Numerous individuals and entities now affix maven or mavin to assert their expertise in a particular area.

The following is an extract from The New York Times, the newspaper in which Safire wrote a regular column about language issues (called On Language) until his death in 2009:

Though he jokingly anointed himself “Usage Dictator,” he was never comfortable with expectations that he play the part of language absolutist, handing down infallible decrees. “Maven” was a title more to his liking, a Yiddishism that he said contained its own “note of self-mockery.” (An incurable paronomasiac, he also enjoyed punning off the word, as in his 1993 collection of columns, “Quoth the Maven.”)

And further:

As battles raged between prescriptive grammarians and descriptive linguists and lexicographers, Safire more often than not played both sides against the middle.

Note: The On Language articles in The New York Times were continued for a while by maven Ben Zimmer, who is also a regular contributor to Language Log.

You could call her a casual computer user.

Casual

(1) : feeling or showing little concern : nonchalant (a casual approach to cooking)

(2) : lacking a high degree of interest or devotion (casual sports fans, casual readers)

(3) : done without serious intent or commitment (casual sex)

(Merriam-Webster)

Someone who's casual about something does it but is not really passionate about it. In contrast, a computer nerd or geek uses computers and is passionate about them as well.