Text descriptions of the belly getting in the way might be cool. Does she struggle to hoist herself up off the couch? Does she have to pick up her belly and rest it on the edge of the sink to do dishes? Does her doctor comment on how unexpectedly fast she's growing, and does she confide that she's also been stuffing herself?
Is different clothing outside the scope of the game? I don't know anything about programming, but if she started out fully clothed, she could shed layers to emphasize growth. Maybe at a certain level her shirt would be too short, exposing the underside of her belly. She could unbutton her jeans. Eventually, the shirt wouldn't stay over the belly at all, and she'd have to wear the unzipped hoodie we see in the current game. She might wear one of those belly support bands, then outgrow even that. Different poses could also be fun. Maybe her posture changes as her center of gravity shifts, or she rests her hands on her belly, or puts a hand on her lower back.
I think she gets plenty big, but it would be nice to see how that growth affects her.