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:

You have to remember the すべ part, which is an admittedly difficult sound to remember. You have to think of the concept of all or entire. When you think of that concept, think of someone's entire fortune. All their money. You want to get all of Beth's money, so you sue Beth (すべ) for all she has.