YA novel ?90s freeing big cat from private zoo

Book I read in the early 2000s, going by language I'd say it wasn't very old at the time. Main character who I'm sure at least one character called Cat, occasional chapters involve her fighting with a therapist. Events take place over a summer where she falls in love with a boy I'm sure is named Jeremy Hook, then when his spirited older brother turns up they hatch a plan to free a big cat from the private zoo Cat works at, then it all goes wrong. Thanks.