Thank you for your question!
To help determine her level, you could view the sample pages for 2nd grade spelling, which would be My Catholic Speller A and give these to her to test her level. You can also go online, and find spelling tests that will help you pin point your daughter's spelling level. Another option is that you can contact your local school district, and they can also administer a test that will give a good idea of where your daughter is at academically. You should trust your instincts, as well. If you think she is ready for 2nd grade spelling, then you should start her there. It is important to present her materials that are neither too easy, nor too difficult.
God bless you and your family!