The only way to do this is to properly go no contact (so change your email etc, she shouldn't still have it if you are no contact) and if she's not taking you seriously when you tell her you don't want contact, get the cease and desist letter previous posters have mentioned.
From experience, I feel it's better to have a solicitor write it.
Especially as she seems to still be getting a reaction from you. If the letter comes from you personally, she will think it's just another boundary she can walk over. It's harder for her to think that if the letter is on headed paper from a solicitor.
Plus, from when we looked into it, any other response from you can actually be seen as inviting more contact from her, perhaps even as harassment of her by you, even if all you have written is "I don't want contact from you any more."
Better to get this done properly and make sure the wider family are aware that you don't want them passing on your contact details to her, or passing on gifts and messages from her to you.
Make sure you properly document every contact. It's easy to save emails from her in a harassment file, but if anything else arrives by post, photograph it (with her writing clearly shown) make a note of the date, time, photograph the contents, write a short note about what happened and how it's effected you, email it all to yourself so you have a date stamp for when it happened, and then bin the lot.
Don't keep food you don't want and won't use in your cupboards for six months, put it straight in the bin. Same with the plates and anything else she sends. If you don't want to throw it away, give it to the charity shop. But don't keep it beyond taking the photographs.
Weirdly, if you are serious about going no contact, it's better to receive the post so you can log it and have evidence of her harassment than it would be to have the post office just dispose of it for you, as you wouldn't have a record then.