Yes, it is correct. It would be an appropriate comment to make in this situation:
Good morning. Could I speak to Anna, please?
She's having her lunch now, but she'll be back at her desk by two o'clock.
Thanks. I'll call back later.
In this context, both 'her' and 'now' are appropriate. The 'her' suggests that it is her lunch break which she is entitled to, and the 'now' emphasises the difference between the present moment when she isn't available and a later time when she will be.