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When Ireland Basinger Baldwin signed her first professional modeling contract in March, the 17-year-old daughter of Alec Baldwin and Kim Basinger had high hopes. Not only does she aspire to some day grace the cover of SPORTS ILLUSTRATED's swimsuit issue or pose for Victoria's Secret, but "I want to be an inspirational model," says the 6'2" teen. "I want people to look at me and say, 'Wow, she looks healthy.'"

But since announcing her new career with IMG - the same agency behind Gisele Bündchen and Kate Moss - she not only has experienced the encouragement of fans, she's also heard her fair share of snark on the Internet. "I have received nasty e-mails, messages on Twitter and ridiculous comments not only about my size but my family," Ireland tells PEOPLE. She reached a breaking point in April and posted an open letter on Tumblr saying, "I understand that I am not a size .008. What I don't fully understand is, what is the good in commenting on a photo of a 17 year old girl calling her fat, ugly, etc?" Of the backlash, Ireland admits, "I didn't expect it. It was really surprising to see how negative people can be towards someone they don't even know."

Ireland is no stranger to negative attention. After Basinger, 59, and Baldwin, 55, ended their eight-year marriage in '02, a toxic custody battle ensued, culminating in 2007 when Baldwin left a scathing voicemail for Ireland, then 11, calling her a "rude, thoughtless little pig" for missing a phone date. He immediately apologized, saying, "I have been driven to the edge by parental alienation." For Ireland, the ordeal was "blown out of proportion," she says. "People make it out to be so dramatic. My dad and I are very tight-knit, despite what people may think." As for the tension between Baldwin and Basinger, "my parents always manage to work things out," says Ireland. In fact "my parents can have each other over for Thanksgiving just to make me happy. The coparenting is intact."

Soon, however, Ireland will have to share Dad's attention: He and his wife, Hilaria, 29, are expecting a baby girl this summer. "I have always wanted a sibling! I'm so excited to meet my sister. I want her to know that I'm here for her whenever she needs," says Ireland. "I love Hilaria. She saved my dad, getting him in amazing shape. And she brought him out of a bad place of being lonely." When it comes to the father-daughter relationship, "even though I don't see him all the time, when we do see each other, it's very special," she says. "He's the best shopping buddy. He goes, 'Ireland, that doesn't fit right.' Or 'I don't like how the pockets look.' He knows women's clothes."

So does former model Basinger. "I love stealing my mom's clothes," says Ireland. "She has a pretty phenomenal Sarah Jessica Parker closet! She and I have dance parties in the kitchen. We're best friends." She's not even fazed when Basinger bugs her about curfew during dates with her boyfriend, stand-up paddleboarder Slater Trout, 18. "Mom will call and be like, 'Are you coming home now?' And I'm like, 'I left 30 minutes ago. Relax!'"

An "awkward and lanky" kid growing up, "I have been on sets with my parents since I was a baby," says Ireland, who will finish high school through an independent study program. While college isn't out of the question ("I want to study creative writing") and acting is "in my sights," for now "modeling is something I want to try," she says. "I'm pumped I get to travel, meet new people. The path is so unclear, but I am excited for what lies ahead."