My ex-T took a year, and then only came back part-time and stopped seeing clients with complex trauma.
My current t (who took maternity leave for both of her children before I began seeing her) took a year for every child.
As hard as it is, it is also an opportunity to do some different work with a different T. Every T has strengths and blindspots. WHile your T is away you could work on some other challenges you experience before returning to your current T when she comes back from maternity leave.
I stayed with the T I went to when ex-T went on leave. This T has turned out to be much more helpful to me because of her different style.

don't panic. It's hard and challenging when T goes away for a time, but there are some benefits to it as well ,even though it probably doesn't feel like it at the moment.