Some Protestants feel compelled to give 10% of their income. As a Catholic, I have never been taught to do this. The subject came up recently because my daughter is about to start a new job and one of her friends told her she should give 10% of her paycheck to the Church. Incidentally, she will be making a gross of $7.00 per hour and has a 2-year-old daughter to provide for.
Tithe was a requirement of the ancient Israelites under the Old Law. Catholics are no longer bound to the Old Law because of Jesus death on the cross. The Church, with its authority from Christ, requires Catholics to give to the support of the Church according to their means (and not just monetary means but also means of time and talent). If your daughter gives what she is able to give, she is meeting her obligation to support the Church. And, if she needs to, she could either supplement or substitute monetary offerings with offerings of time and talent instead.
Catholic Answers Guide to Family Finances by Philip Lenahan