Use singular they. Thanks to Mark Summerfield.
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 0069052..ae2dbf3 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -814,7 +814,7 @@
Python.
The highest possible limit is platform-dependent. A user may need to set the
- limit higher when she has a program that requires deep recursion and a platform
+ limit higher when they have a program that requires deep recursion and a platform
that supports a higher limit. This should be done with care, because a too-high
limit can lead to a crash.