No. The only thing you can do is to mark her as living. Her existence will still show up to anyone who can see your tree, but her name and facts will not. It will show gender and relationship to others in the tree.
If your tree is public, random people will not see names/etc of living people. For anyone who is subscribed to your tree (someone you invited), you can go into settings and mark whether or not that person is allowed to view living people. The default is for it to be turned off.
If the issue is that you don't want your tree to show that some of the children in a sibling group have a different mother, then none of this will help.
This is one of the reasons I have my main tree on my home computer. If I know a family secret and have a fact or doc for it, it goes on my tree. But my Ancestry tree is public (and smaller because I only add to it if the info comes from an Ancestry doc).