Why it is not used?

Question

Katherine Brynat joined Purcell Firm forty years ago, making her one of our longest-serving employees since the firm was first established.

i'm a foreigner.

In this sentence , "her"

Why reflexive pronoun is not used ?

Answer 1

"Her" has two meanings. One is the reflexive pronoun, that is, with the sense of belonging to the person concerned.That is not the sense here.
The other use of "her" is as is the accusative of "she". In this sentence, Katherine Brynat is the object of the sentence. There is no subject, but the notion conveyed is the fact of her having joined the Purcell Firm and this fact makes "her" a long serving employee.

Answer 2

Hello there!
A reflexive pronoun is not used because it would be redundant, repetitive.
In other words, the sentence would be read like this:
Katherine Brynat joined Purcell Firm forty years ago, making Katherine Brynat one of our longest-serving employees since the firm was first established.
I hope this helped! :)

Answer 3

Reflexive pronouns are for things we do to ourselves: I wash MYSELF. In the last sentence MYSELF is capitalized to show it is a reflexive pronoun. She washes HERSELF. In your example her is in the objective case. Her is the object of the verb making. It can't be reflexive because she did not perform the action (in the grammatical sense). Of course in the real world sense she made herself the longest-serving employee, but we don't talk that way. Probably in your native language you wouldn't either.