<human>: Give me the gist of the text in a nutshell

The way my sister is acting is kind of concerning, but I have no idea how to get through to her. My mom checks her phone regularly, which is how I know all of this. 

It all started two years ago when my mom caught her talking to boys she met online, telling them she loved them, and sending out tons of pictures of herself in underwear and saying things like "Ugh I'm chubby but here you go." 

Over the past few years she has been getting in trouble for sexting (not pictures AFAIK, just dirty talking). 

This year, she got her first in-person boyfriend. He was a grade older. They dated for about 3 months. Notable things: they made out in the back seat of his parents car while his parents were driving them home from a movie. She broke up with him because she didn't like him anymore, and also because he kept trying to convince her to give him a blowjob while she didn't want to (GOOD! I'm proud of the way she handled this).

A couple months ago, immediately after breaking up with the first one, she started dating another guy who is 18! Way closer to my age than to hers! After about a week they started saying I love you, blah blah blah. I thought they were still together, but last week I saw on her phone that another guy was texting her hearts and kisses and stuff. I asked her what she's doing, and whether this means she has two boyfriends now. She said she's not dating either of them.. even though she says I love you to one, and calls the other one babe. The new one is also at least 17. 

Yesterday I came home to my mom telling her that she checked her snapchat and found boy(s) sending her dick pics, and that she can only imagine what my sister is sending them. They didn't have a talk then because my dad was coming home and my mom didn't want him to find out (for my sister's sake).

It seems like she gives in to anyone giving her attention. What can I say to her to discourage her from behaviour like this?
<bot>: I think my sister is the "easy girl" of her school because she does not have much self respect. I've tried talking to her, but don't know what to say to help her.