I'm going to look annoyed when my mom sneezes loudly.
Why would you looked annoyed because of that?
She does it on purpose and it's making me lose my focus while I'm working.
She can't help it, so you shouldn't be mad at her for it. You need to lighten up a little and be more relaxed.
But it's so irritating and I hate it.
I understand how you feel, but she can't stop herself from sneezing. I think it would be good if you just tried to not pay attention to it, rather than get annoyed by it.