。
Even calling her a singer is generous — she's pretty bad.
Literal
She [topic-は] singer [even-though-saying-といっても] poor thing is.
~といっても = 'even though one calls X / even saying X.' It concedes a label only to qualify or undercut it: 'sure, you could call her that, but…' お粗末 means 'poor, lame, ill-prepared,' often in mock-modest or critical contexts (the polite お- is a marker of self-deprecation when applied to one's own offering, but it can also be straightforwardly negative when used about others). Wrapping the verdict in ものだ ('it's the kind of thing that…') gives a generalizing or summing-up tone. The whole sentence is a tactful-but-firm pan.