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Hold up... first, is this photo for you or the client? If it is for the client, ask them what they have in mind for the photo, end use of the photo, etc.
If the client tells you that they want to use the photo for social media, website, they just want a nice photo of them, etc., then you have an idea of the intended use.
If it is sell bikinis for plus size people, then you don't have to worry about making them look thin by asking to suck in. If they want a photo that isn't for a product and maybe for a dating site or portfolio, then you shouldn't be worried about asking to suck in.
Also, try to use a zoom lens with a focal range of 105 mm or higher. 200 mm is probably best if you are doing portrait. Using focal lengths under 85 mm tends to gives a roundish look.
If you are shooting wide angle, then you are really just capturing them in the scene, not focused too much on body I would think.