Suggested materials for eulogy for a mother are available at LoveToKnow.com. In addition, Write-Out-Loud.com and TheFuneralSite.com both provide guidelines and templates for writing a eulogy.
LoveToKnow.com suggests reading some of the deceased mother's favorite passages from literature, especially any poems she loved. If the mother was religious, it's also appropriate to read scripture. Recommended passages include Psalms 23, 27, 19, 91 and 112. Another idea is to write a letter to the deceased mother for reading at the funeral.
In preparing to write a eulogy, TheFuneralSite.com recommends gathering information about the deceased person, brainstorming ideas and topics for the eulogy, and organizing the material.