Child travelling with grandparent

My daughter is flying allegiant with her grandma. She is 18 months old and her grandma will be on a flight from point A to B, pick up my baby at point B and get back on the same plane to go back to point A. Can I go with her to the gate to await their arrival? If she is an infant on lap and does not have a ticket will this be a problem? Can I check a stroller and car seat for her and then go through security to meet the family by the gate? I have called the airline multiple times and don’t know what this process looks like. I know families do it often so just looking for advice! Thank you in advance.