A question about permissions.....might be a bit 0T

Hi, I installed OSCommerce for a client quite some time back and everything was running smoothly. When the client needed to make changes she used to tell me and I used to do it by ftping in, dl'ing the files, making changes, uploading them. Now she found that in the control panel you can edit the files yourself...but when she tried it told her that the right permissions are not set for that...it only seems to be working is if its chmod'ed to 66* or 777, I have no problem with handing over full control to the client but if i chmod all those files to 66* or 777 and she gets hacked shes gonna blame me...so my question is...is it safe to do that or tell her shes just gonna have to learn FTP if she wants to do it? Its presently on 644. Thanks, -Ryan