First, Vicky sets the normal permissions to allow only her to access her file. Then, she'll set the ACL:

[vicky@localhost marketing]$ echo "This file is only for my good friend, Cleopatra." > vicky_file.txt

[vicky@localhost marketing]$ chmod 600 vicky_file.txt

[vicky@localhost marketing]$ setfacl -m u:cleopatra:r vicky_file.txt

[vicky@localhost marketing]$ ls -l
total 4
-rw-rw-r--. 1 charlie marketing 0 Nov 13 15:59 charlie_file.txt
-rw-r-----+ 1 vicky marketing 49 Nov 13 16:24 vicky_file.txt

[vicky@localhost marketing]$ getfacl vicky_file.txt
# file: vicky_file.txt
# owner: vicky
# group: marketing
user::rw-
user:cleopatra:r--
group::---
mask::r--
other::---

[vicky@localhost marketing]$

There's nothing here that you haven't already seen. Vicky just removed all permissions from the group and from others, and set an ACL that only allows Cleopatra to read the file. Let's see if Cleopatra actually can read it:

[donnie@localhost /]$ su - cleopatra
Password:

[cleopatra@localhost ~]$ cd /marketing

[cleopatra@localhost marketing]$ ls -l
total 4
-rw-rw-r--. 1 charlie marketing 0 Nov 13 15:59 charlie_file.txt
-rw-r-----+ 1 vicky marketing 49 Nov 13 16:24 vicky_file.txt

[cleopatra@localhost marketing]$ cat vicky_file.txt
This file is only for my good friend, Cleopatra.
[cleopatra@localhost marketing]$

So far, so good. But, can Cleopatra write to it?

[cleopatra@localhost marketing]$ echo "You are my friend too, Vicky." >> vicky_file.txt
-bash: vicky_file.txt: Permission denied
[cleopatra@localhost marketing]$

Okay, Cleopatra can't do that, since Vicky only allowed her the read privilege in the ACL.