Travel while waiting for visa renewal

Hello so my aunt would like to know if it's possible to travel outside the country while her visa is still in the process of renewal. She went to the immigration in October and since then she hasn't gotten the postcard, and has already bought a plane ticket for the 23rd of December.
Because she was expecting that the postcard would come in a few weeks but it still hasn't and her visa is going to expire on the 17th of December. I would really appreciate any help thank you very much.

It's okay as long as she has a re-entry permit that covers also the two-month "extension" period after the end of the normal period of stay, so confirm that with the immigration officer that will grant the permit (typically at the exit immigration control for short trips).

It could also be a good idea to inform immigration of the trip so they won't send the postcard while she's away.