She's not much to look at, but she's got a lovely personality.
be not much to look at
A euphemism to describe someone deemed physically unattractive. Jack's a nice guy, he's just not much to look at, you know?
not be much to ˈlook at
(informal) not be very attractive: The boat is not much to look at but it’s easy to sail.He’s not much to look at, but he’s got a great sense of humour.