Quote: "I would opt for Wordpress but I'm not aware that It can be easily embedded into an existing template.
Any ideas would be very much appreciated, thanks."
There's a few tutorials for integrating WP into an existing site, this one looks good (well, the one it links to):
http://idratherbewriting.com/2008/12/28/integrating-wordpress-into-an-existing-website/
But if you want to skip WP altogether, check out https://sourceforge.net/projects/sphpblog/
WP would offer a fair few more features though
Depending on what your client does, she may find the features of WP to be compelling enough to pay you for a WP customized theme.
Just remember with WP, it's a resource hog, install a cache plug immediately before moving to production