Incorrect spelling, explanation: this form, refering, is incorrect since we should double the last consonant (according to a rule, that when a word ends with a combination of consonant-vowel-consonant, then the last consonant is doubled in case of adding any suffix to the word. Therefore the correct form is referring.

Correct spelling, explanation: referring is the word refer with suffix -ing. As refer ends with a combination of consonant-vowel-consonant, the last consonant, r, is doubled. This is a common rule when adding a suffix to a word. This way the correct form is referring, not refering – the r was doubled.

Definition of referring:
verb, “-ing” form of “refer”; to redirect the meaning or attention to sth else; to direct to sb
In “Gilmore Girls” they are constantly referring to old movies, I love it!
For me, referring to your mother-in-law as “mum” is totally normal.