The concept of a doclink in a web application don't exist. Therefore you must create an email and include a URL to the specific element. Not sure if using XPINC allows adding of a doclink.
email = database.createDocument();
email.replaceItemValue("Form", "Memo");
email.replaceItemValue("Subject","Test");
email.replaceItemValue("Body","You have email");
email.replaceItemValue("SendTo", sendto);
email.send(false);
In the past what I have done to include a link was to reconstruct the URL, as shown below, for the XPage and add that to the body of the message.
I used a viewPanel link for my scenario, but this should get you down the proper path.
var url:XSPUrl = context.getUrl();
var doc:NotesDocument = row.getDocument();
var unid = doc.getUniversalID();
var scheme = url.getScheme();
var host = url.getHost();
var db = database.getFilePath();
pdfurl = scheme + "://" + host + "/" + db + "/0/" + unid;