Guests wasting food

She clearly pisses you off so why invite her?

Smaller plates

And ask her to bring a bottle of wine

well no, if it's not on her plate then it can be eaten by someone else or can be leftovers or frozen for another day.

We bbq for family most weekends and cook a bit more so we have chicken or prawn or whatever for a lunch in the week. If there's any left.

I like this. A polite way of drawing her attention to the matter.

If it bothers you and you can’t just ignore it then I think the suggestion of cooking things gradually is a good idea, rather than everything being available at once. I do think when everything is out at once, and people are hungry, then people can be more likely to overload a plate because everything looks good and when you haven’t yet eaten your eyes can be bigger than your tummy. If you put things out gradually then it prevents that “omg I’m starving I want 3 of everything” because they can have a couple of sausages in a bun, sit after that for a bit and then have a burger, sit for a bit after that and usually once they’ve actually eaten that huge appetite urge to eat everything goes.

I do get the annoyance though. There are 2 particular people in my extended family who do this at every family party/wedding/christening/wake, they go to the buffet with 2 plates, one for savoury and one for sweet, load both of them up with enough food to feed a whole table of people, and they end up leaving what would be a normal persons portion of food on the plate.

This is not something to get worked up about. If you are worried about food waste don't host a bbq in the first place and certainly don't start policing other people.
At buffet type events people often take too much and end up not finishing it. Perhaps they think they'll take a bit more so they don't have to end up going up and down all the time or they over-estimate how hungry they are or they take something and don't like it.
Get smaller plates as many others have suggested that means people can't load as much on and serve the barbecued food in stages so it isn't all ready at once.

And then you'll have to ignore it. If you let things like this piss you off it just means you end up feeling shit and that's no way to live your life.
If you don't want people throwing your money in the bin then don't host a bbq.

Sorry @Hoppinggreen , cross posted!

I hate this obsession with 'wasting food'. If she eat it all, anything that is more than essential for her is also wasted isn't it?

Your money's been spent either way. Supermarket isn't going to buy back what is not consumed.

You can’t just serve her. Serve everyone if this is the hill you’re going to die on, but realistically suck up the one plate of food waste, it’s what’s happens when you’re hosting, you’re always going to end up with some

Not being flippant, why not get smaller plates?

Smaller plates or just let it go

Let it go

and load up her plate into a container to take with her

I'm guessing there's a whole load more to this, and that you really don't like this person. Also guessing it's a family member/inlaw..?

Put out the cheaper food like bread, pasta salad etc for people to serve themselves and just accept that there will be some wastage of those. For the meat I would cook a bit at a time and then serve it when it’s done, if she’s coming up for sausages but hasn’t finished her burger then it’ll be easier to just say ‘Oh, I’ll keep a sausage aside so it stays warm while you finish your burger’ but not actually let her add more food when her plate is still piled high. There may still be a bit of waste but hopefully not as much. You could also use smaller side plates instead of big dinner plates so it’s not easy for people to pile them high with food they won’t be able to eat.

How can this even be a thing? Why do you host people of you are watching what they eat and throw away? If it bothers you that much, don't invite her! How much can one person really waste anyway??!

Is smaller plates an option?? My dinner plates are huge so we use the side plates for BBQ’s. But we also cook in stages, so not everything is ready at the same time.

This would annoy me too but realistically I think you need to let it go. Or have tiny plates

Any chance she likes being 'looked after'? If so, you could show her to a chair and offer to go get a plate for her?

Use small plates! Means people can't take too much in one go.

she is your guest!

The alternative of course would be to make nicer food.

That's pretty nasty.

And how is offering a doggy bag rude?
I think she is the one being rude by only eating a small amount of the food on her plate.

It really annoys me people's casual attitude to food. Admittedly I don't eat meat but seeing people just throw meat away so casually makes me think about the poor animal needlessly slaughtered just so they can be discarded in a rubbish bin.

I'd either let it go or change how you BBQ and serve everyone. Just serving her isn't going to stop her from getting up and helping herself to more food if that's what others are doing.

It’s just one plate of food at a BBQ. You need to let this go. It bothering you is a you problem, and you’d be petty to impose your food ideals on an adult guest.

Besides, maybe she ends up not eating it all because the food is shit and she’s trying to be polite by taking some instead of turning her nose up. I went to a BBQ once and was faced with many dishes that had mayo in them that had obviously been left out too long, a burger that wasn’t fully cooked. So despite intending to eat a full meal, I had to pretend pick at food to not offend my hosts by making their lack of food safety and hygiene into an issue,

Dear god what a joyless host.

If you’re happy serving sausages and burgers you’re not the environmental warrior you think you are. Be a gracious host.

The suggestions to give her a doggy bag!! I can’t imagine being so rude.

The alternative of course would be to make nicer food.