You do make a very good point, that said she has been very honest about the surgeries she's gotten done, in her youtube channel there's a QnA where they ask her if she's natural, she says do I look natural? I've been very honest about getting lip fillers and my boobs (her face also looks different, dunno if just lip fillers could do that), so no I'm not natural. Paraphrasing but you get it. She could hide the BBL and be honest about the other two, I don't see the point but she could be doing that.
Her ass could be becoming more fatty and that's why it looks that way (you can see she has a bit of cellulite there), could be diet, hormones, birth control, any number of things can cause it to get bigger on top of her gym routine. It has gotten much bigger compared to when she started OF, even if it looks natural to me, I'm no expert.