AIBU to object to neighbour using my garden as their main access?

Put a lock on the gate and tell her the only access she can have is to put the bins out once a week otherwise it will stay locked.

I find it unlikely that this access was intended to allow use as her main access, although it may of course be poorly worded. She sounds as though she is really abusing it

They may have right of access but this usually only pertains to the residents of the property. They are creating an unnecessary burden but asking everyone to use their back door, and the sign is a clear indication of this. The only time a person should use your garden acres (like Royal Mail) is if their front door is inaccessible.
So, first: check your deeds to understand exactly what are the limitations of the access.
Photograph the sign they have on their door. Send them a letter about not having anyone other than themselves use this access, and only within the limits specified. Say the constant stream of unauthorised visitors has created a security risk and lack of privacy etc. Keep a copy - you must create a paper trail.
Put up a sign in your gate/fence saying this is private property and all deliveries for number X should go to their front door.
Of they refuse to cooperate then you may have to escalate it via a solicitor (try the one you used for conveyancing).

Why don’t they use their front door like normal people? Sounds like CF behaviour and needs to be squished.

Sounds like they are over using it. Normally it’s a right of access for things like bins and ground works. Not just the postie and such. I’d get it checked.

Also see about fencing in their access to it doesn’t affect you as much if it’s the bottom of the garden.

Check your deeds, most easements only apply to the dominant tenement ( the people who live there) and not third parties - i.e. delivery drivers. You say it's been a year - have you not spoken to her seriously in all this time about your right to privacy?

Boundries! Now.

Check the wording on the deeds. It is unlikely that the easement can be used as the main entrance.

Same arrangement when I lived in a mid-terrace. We also had to allow emergency access.

Your situation is completely untenable as you have no privacy in your own garden and this could also affect your home insurance as so many people have access to your property. Check your deeds, it's likely that your neighbour is knowingly taking the mick.

Given previous history though expect a fallout when you stop the thoroughfare.

We pulled out of buying a house once we realised next door would have to pass through our back garden in the manner you’ve described. We were reassured she was a single woman who only used it to bring her bin in and out once a week but I worried about what would happen if she moved out and someone completely unreasonable moved in. I can’t believe your neighbour can’t see how mental it is that she’s directing everyone into your private garden! What is the shame of using the front door?!

Yep, check your deeds, and then check your home insurance to see if you have a free legal helpline that you can call to establish what rights you have to take any action.

Having the backing of legal advice will mean that any approach that you take is likely to be not effective, as it will limit any argument on their side.

Check your deeds. The two people I know, who live in mid terrace houses, only have right of access through their neighbours' gardens to put their dustbins out.

Is your garden big enough to section off a "path"(wide enough to drag a wheelie bin along) at the edge/end to her garden so your garden remains secure?

The access presumably is for them not for almost and sundry? So I would personally lock the gate and not allow access unless by arrangement ! But I am grumpy even though the weather is nicer !