I don't like this

[Dumpylump]

I'm not sure how I feel about this, so I wondered if writing it down might clarify things in my own head. Apologies if it's long....and it'll probably be boring.
Dp is a manager in a large company, he has been there for several years. There is an admin assistant who works there too, who is becoming a little over friendly I think.
We were at a big party a while back - to which some of the people from dps work were also invited, admin amongst them. Alcohol was consumed - too much in the case of dsd, who got a bit tearful and teenage drama-ey, and so I went with her to the loo to tidy her up, and sort her out. Admin elbowed her way into loo, and commented on the situation, then later apparently told dp that I had been really mean to dsd. Neither dsd or I, thought that I had been mean, she went off to enjoy party with her friends and gave me a hug - all witnessed by admin.
She also told dp that I had been bitching about other people at the party (not true), and that "I didn't seem to have a good word to say about anyone".
Dp asked me about this in quite a confrontational way and we ended up arguing, and I went home.
We had a long talk about it the next day, he apologised and I pointed out that if someone I knew who had only just met him started talking about him to me, I would stand up for him, not immediately agree and seek him out to explain the error of his ways to him!
Admin is on his Facebook - as is pretty much everyone in his office, which I think is a bad idea anyway - and has taken to commenting and liking pretty much everything he posts. If I post something and tag him in it, she will like it, without even acknowledging my existence.
She has posted remarks like "ah, you did x at the weekend like I suggested", or "I told you dsd would enjoy x".....again without even acknowledging that dp has tagged me in his post.
I'm starting to wonder if she is just friendly, (although clearly not towards me), or if she has designs on dp, or am I just being silly.
I have no reason to think that dp is interested in the slightest, and yet I still feel threatened and a bit sick.
And now that I've written it down, I sound like a daft wee girl, and I don't feel any clearer about it!

You are his partner and she is just a work colleague. I'd have a very stern word with him and tell him to take his work people off of his facebook. Is she a threat, yes she is. Why does anyone at work (unless they become friends privately) need to be there? In saying that it sounds like he's also encouraging this. Do not let him minimise what's going on. You are not making a mountain out of a molehill. I personally would be furious with him.

Of course he knows what's going on! He is enjoying the attention ! How would he feel if it was the other way round and it was a male colleague trying to Wendy him!

You need to have a very frank discussion with your dp and gauge his response. Even if he pretends feels your imagining it, he still should be active in assuring you that things are all good from his point and Wendy can fuck off.

Good managers don't let work muddy the home. Clearly in terms of performance he must be doing well, but managers read people, he's not reading you or this other woman very well by your account.

Twice in my life women have slagged me off to my husband.

The first time he told me all about it and I dealt with her directly (she was someone we both knew equally). The second time, the woman did it whilst I was in ear shot and she got a stern talking to by me too and has shut her mouth ever since (though makes it clear she dislikes me, but the feeling is entirely mutual). On both occasions my husband had my back.

Your DH's boundaries are the problem and you need to talk to him. He can block her on FB, her shit stirring at the party would be justification enough.