The fact that she has so much leave saved up implies two thing. 1. she's been doing this for a long time, and 2. she usually leaves almost immediately after the mission was completed. (In the first world she stayed in, she only stayed until her son grew old enough to gain right to the throne)
The fact that she's using 50 more years just to stay with him even if there isn't any use for it means she really does love guys like Gu chen.