That woman’s face is beautiful but her heart is ugly.
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of ugly? It's ugly still!
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.