1. What definitions can I refer to the meaning 'complementizer'?
There's little agreement among grammarians on how to categorize the core 'function' words in English; but the term complementizer is generally used only for words which introduce clauses. According to the SIL Glossary of Linguistic Terms
A complementizer is a conjunction which marks a complement clause.
And the Lexicon of Linguistics at the Utrecht Institute of Linguistics defines complementizer as an
element introducing a subordinate clause
CGEL† doesn't use complementizer at all, but it does use subordinator in a very similar sense. It recognizes only five subordinators: that, for, to, whether, if. You should note, however, that CGEL regards to as a subordinator of VPs, not clauses, and that CGEL categorizes most of what traditional and many contemporary grammars call subordinating conjunctions as prepositions.
(skip this unless you're really fascinated by grammatical theory:)
There is very little consensus among contemporary grammarians on the terminology for the 'function' words. Many of these words in fact serve multiple syntactical functions not only across utterances but even in individual instances. Consider, for instance, this sentence:
I haven't yet decided which theory I will follow.
Here which acts as (a) a determiner on theory, (b) an 'interrogative' in the sense that it points to a gap, a blank to be filled in, (c) a 'subordinator' in the sense that it marks the following clause as subordinate, and (d) yes, a 'complementizer' in the sense that it marks the following clause as a complement of the verb decide.
And I can readily imagine a grammarian generalizing the SIL definition to include words which mark entities other than clauses as complements. For instance, an of PP following a noun derived from a transitive verb usually marks its object as a complement of the noun rather than a modifier—the 'direct object' of the noun—
the conquest of Granada means "the act or fact of conquering Granada"
So in this case the preposition of could be said to act as a 'complementizer'. ... That's sort of far-fetched; but it points up the fact that in the end, complementizer (or any other grammatical term) means whatever its user's particular approach to syntactic analysis needs it to mean.
2. Can I refer words like 'her', 'its' to the meaning 'complementizer'?
No. In your examples her and its are not complementizers but possessive pronouns acting syntactically as determiners—which is another multivalent term about which scores of articles and many entire books have been written.
†Huddleston and Pullum, The Cambridge Grammar of the English Language, 2002