No you don't, actually.

She's got the flip side of the objectification coin. She's used to not being seen and being overlooked for skinnier girls who fit the marketed body type aesthetic.

Logically, your first step is letting her know that she's seen.

You do this from afar, by mimicing the same sort of tactics girls use to get boys' attention.

You'll have to do this several times, biding your time because she's used to not being seen or being the butt of some bad taste 'joke'. She's gonna need to see some repetition.

Once you get a positive response, then you approach. Take it slow. Ditch the cheap come ons. Talk to her like a person.

Examples of getting her attention.

Put yourself in her path till she notices you. Then smile. Maybe compliment what she's wearing, even if you're across the room you can gesture to your own shirt or something then point to her and thunbs up with a wink or something. Or raise your glass as though you are toasting her from afar. Even just a head nod.

You can walk by her, make eye contact and smile.

Send her a drink with a napkin that says something like, "to the prettiest woman in the whole room from the enamored guy in the green shirt". She'll look for you. When she finds you, smile and gesture to a seat or spot next to you. If she's curious, she'll either come over or gesture for you to join her.

Keep it cool. Keep it light. Be respectful. Be playful.