Good for you... I go there often. Some of it is out of my league as it's more specialist US based stuff - but where I am able to I often respond to her questions. No disrespect to this section, you have to admit that Rosie is more active and more prolific - so there's more to answer and contribute to.
Even though you are grammatically correct on that, expressions such as hers and others similar to it are accepted by most in informal conversations. Example: Where's he at.