Instead of setting these programs to load on startup, they usually have an
option to turn that off.  Then, if your daughter wants to chat she can
either access the program from the start menu or a shortcut she creates or
that possibly was created by the application.

I can't tell you specifically where the option is as there are many
different chat programs but open the program and check the toolbar menus for
options and/or preferences, you will likely find an option to start with
Windows that has been selected, deselect that option.