Maybe. It's normal for siblings (and moms) to go through a range of emotions when baby number two joins the family. Your toddler might be proud, curious, confused, excited…and, yes, jealous. Family dynamics change, and everyone has to do a little adjusting. Before baby arrives, it can be helpful to teach your toddler about babies, how they act and how they look, and let them know that they need to nurse a lot. If your child isn't still nursing, explain it to her. Show her pictures, and let her be around breastfeeding babies. (If she is still breastfeeding, talk to her about tandem nursing.)
When baby arrives, let your toddler be a big helper when you are breastfeeding. (She can bring things to you, like the phone, remote, or a water bottle.) You can also give her attention while you nurse by reading with her, playing games (Simon Says works well), singing songs, or telling her stories about when she was a baby. Just strategically place a pillow or two so that you have a free hand.
It's also okay to let your toddler do her own thing while you breastfeed. Set her up with activities that don't require your help, and feel free to take time to focus in on baby (and mommy).
It's normal to feel guilty for bringing big changes into your toddler's life, but give yourself a break; baby and toddler will be a huge, wonderful part of each other's lives.