if you truly mean just your girlfriend, the great thing about wondering things about your girlfriend is that you can ask her directly. strangers on the internet will probably not provide useful answers specific to your girlfriend
more generally, i think there are a few common reasons people go shopping/hang out in stores - most areas nowadays lack third spaces (article about this here), consumerism due to the internet/influencers and/or escapism (which i think “retail therapy” does fall under). the ways in which this might apply more to women are, i think, in how we are socialized to see shopping as a feminized and important/rewarding activity, from ads about clothes/makeup to toys that recreate grocery shopping. and then there’s the relationship of buying things and the idea of achieving specific beauty and body ideals; the pressure to conform to norms and look a certain way no matter the price. but just “hanging out in Target” (compared to spending a lot of money there) is probably not that deep.