Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
The most ugly thing you've ever seen was a mini cookie (みにく). Why would any one want a tiny cookie? Cookies should be huge, and enough to fill you up. The more you look at the mini cookie it seems to become uglier and uglier to you.
That woman’s face is beautiful but her heart is ugly.