Is the suggestion here that the visitor to the house brought her own food (etc) just for her own use or that she brought it as a contribution towards her host's expenses?
If it's the former then (unless she's on a special diet that her host couldn't cope with), I'd say that it was a bit of an insult, as it would seem to suggest that the host's catering isn't up to standard. If it was the latter then it might simply be seen as a well-intentioned error.
When I was a child, whenever my Uncle Tom and Aunt Audrey came to visit our house, my uncle would always bring his own sandwiches and then eat them in his car while the rest of us ate our tea in the house. My mother took great offence at him doing that (although she never expressed it directly to either my aunt or uncle), as she saw it as suggesting that her food wasn't up to standard.
Conversely though, if I've been invited to a party I'll usually take some booze along with me (even if it's not been specified as a 'bring a bottle' party), simply to show that I don't want the host to suffer a massive hit to their bank balance through hosting an event that lots of people will be enjoying.