All you really need to do is set up the client on the phone and tell it to connect using the settings they have sent.
So you will need for her e-mail account she wants to connect to
Protocol IMAP or POP3
Incoming server name e.g. pop3.ntlworld.com
incoming port s/b 110
mailbox name on the server e.g.
joe.bloggs55@ntlworld.com
password (case sensitive
Outgoing server - now you will probably need to call them for one of these, though it is probably mail.o2.com or similar.
ougoig port s/b 25
Email address as you would like it show in the reply to box
Then you put them in and off you go.
I would recommend you get GPRS access enabled on the phone if it has it. It makes use of an email client so much better.