My 16 year old niece is pregnant!!!!!?

my Neice Lexi is 16 and has a very nice boyfriend named Ty. Ty is liek any other guy and loves he has been with over 12 girls in 2 years! Lexi was one of them and the first time she was fine and this time shes not Ty got her pregnat and she won't go to her mom or my sister Kelsey. Kelsey has 4 other children to take care of and Lexi dosen't want to tell her because she knows Kelsey will want to take responsability for teh baby. im the closest thing to Lexi's mom and she only confirmed me and Ty. i don't know how to handel this should i handel it in a case like it was my own daughter? or another way? and what should lexi do to get her mom to understand shes an adult and can take care of a child?