Sibling rivalry could start even before the second child is born. It often continues as the children grows old and they start to compete from toys to clothes to their parents attention. It can be very frustrating to parents when this happens. However, this too can be avoided if we prepare our kids on what's to come.
Set expectations. Spend time with your older kid and talk about the changes in the family dynamics should there be another child. You may want to tell her that there may be times that the family would need to cut down on the movie dates, or the trip to TimeZone. You can, however, plan for more activities at home. Tell her that the baby may get more attention simply because the baby can't change clothes or diaper or eat on his or her own. And in any case that mama can't attend to her needs, tatay will be there for her. As an Ate or Kuya, tell her what she can do to help the family out.
Tell stories. You can do this anytime during the day. Tell her stories about how her arrival years ago has changed you and the adjustments you and your husband had to make. Make the story as hilarious as you can. One story that my daughter love to hear over and over again was when she was 3 weeks old. I told her that mama was so tired but she didnt want to sleep yet. So I talked to her, begging her to sleep but she just stared back at me and say "hoo...hooo." Of course after telling the story, you may want to drive your point that there may be days that mama will be really really tired and cranky.
Get her involved in the whole pregnancy period. Make him/her feel that it’s not just all about you and the baby. It's all about the entire family and it's all about him/her stepping into a new role -- that of an older brother or sister.