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:
Who is the one person who always seems to be encouraged and excited? Isabel (いさ)! She's so positive and always cheers everyone, including herself, up.
That horse is acting too lively for me to bet on it.
Koichi and Viet came into the office in high spirits.
The boy left for his trip in high spirits.