Well, this Tammy is, I'm sure, aiming her product at young women. And girls.
I'd say that's she's targeting people interested in fitness and mothers. As you'd expect 
Is there an arse expanding diet you can recommend?
I thought you could so literally typed "what should I eat to get a bigger bum" into Google.
Obviously diet alone won't magically expand your arse cheeks but the right diet with exercise will help.
trulybooty.com/foods-that-make-your-buttocks-bigger-naturally/
www.newhealthadvisor.com/Foods-That-Make-Your-Butt-Grow.html
howtogetabiggerbutt.info/what-to-eat-to-get-a-bigger-butt-a-butt-boosting-diet-plan-for-the-week/
Literally the first three articles that popped up.
I'm not suggesting that women cannot both be attractive or beautiful, and intelligent, what I guess I can't understand is why a woman wants to be looked at in a purely sexual manner. It's the sexualisation of the pose, the big lips etc. that I am struggling to understand.
I don't think taking one photo means she wants to be looked at purely from a sexual standpoint.
From her page I think it's clear that the things she's talking about most are her fitness career and her kids. So I'd say those are the things most important to her.
One night when she was feeling sexy in her underwear or getting £1000 to take a picture in a specific brand of underwear she snapped a photo and put it online.
If she's selling underwear more angled at recreational purposes, she's probably going to go for a pose that looks sexy. Similarly, if the underwear brand is more marketed to that sort of look then that is what she'll go for.
If she just feels sexy, she'll probably post a picture that looks sexy. I don't think one racy picture - which she might have been paid for anyway - suggests she values herself as sexual first and foremost.