To have given this as a gift?

Seriously don’t sweat it. I think what you did came from a good place and i wouldn’t be offended at all. it’s the sort of thing at work we would laugh about and would certainly not be upset about.

How much was actually missing though?

Nah this is lovely. She did you an unexpected favour, expecting nothing in return and you wanted to repay this with something you already had that you thought she'd like. I'd find that absolutely fine and not weird at all. The fact it's opened is not ideal but I doubt I'd notice and if I did I wouldn't care. It's limencello not chicken! She sounds lovely I reckon she was grateful.

I think I'd have said something like, "oh no , I wanted to give you this but looks like teens have been at it" and gone off her reaction. From what you've said of her I expect she'd have said thanks and taken it off your hands.

Hoping she wouldn't notice is a bit off imo.

Just text her and explain the situation. Just say you thought she might have liked it but your dd has since informed you that she did pour a tiny bit from the bottle to taste. Because of this, please feel free to tip it away and you will get her another gift. From the sounds of things she will probably tell you not to be silly and not to waste your money.
Last year my mil bought us easter eggs. She bought one for each of the kids, one for me but nothing for her son (DH). Anyway, she opened mine first, ate both bags of minstrels that came with the egg and still gave it to me and saw nothing wrong with this. I posted about it on facebook and what a numpty she could be at times and my sil blocked me lol. Ah families.
I think there's a difference between gifting someone something you've swigged (or eaten) half of, and a bottle that may not even look like it had been opened anyway.

I have been the recipient in similar situations before and been nothing short of delighted that someone appreciated my help and wanted to thank me. The gift itself is largely irrelevant.

I have long made it point to take things in the spirit they are intended and it honestly makes life much nicer. Why on earth would you choose to sneer at a sincere expression of appreciation rather than bask in the glow of being well thought of?

I love Limoncello!
I think it was a really nice spontaneous gesture. I think if you tell her she will laugh and still be delighted with the gift.

Gosh there are some ungrateful types here. What happened to "it's the thought that counts"? Even if I didn't like Limoncello or thought maybe someone had tried it, OP, I'd still think it was a sweet, generous thought of yours.

You could always say you mentioned it to DC and they said they opened it, you didn’t realise, mortified etc?

YABU to buy Limoncello

Will she definitely have noticed? I wouldn't notice the cellophane missing so it depends how much is gone.

I think bringing in chocolates tomorrow and saying your teenager confessed last night is the best course of action.

No idea why you're getting so much heat for the gesture, a spontaneous (unopened ) bottle is a lovely way of saying thanks for a favour.

I hadn’t eaten any, it was just a type (Stilton) I like but I didn’t want to take a half eaten pot home. I had no idea how long he’d had it etc.

You said you liked it at dinner, he gave you what was left, why did you bin it?

You sound like a thoughtful and kind person OP, and I would have regarded you as such if you'd given me this gift. Regardless of whether or not I liked it or would have made use of it, I'd have still thought fondly of you for the gesture. I hope your colleague does too.

That's coz he hated it so he wouldn't have cared as would have binned it anyway

Exactly. Genuinely delighted then..hmm..is this? Open??? Ewwww

At dinner at a friend’s house and he brought out cheese. I mentioned that I really liked one and he gave me the rest of the pot, really insisted. I fear i binned it. Bit weird.

Mother once gifted someone a half drunk bottle of port for Christmas and laughed it off when she pointed out it was half gone. I’d have been horrified had that been me, the total lack of consideration, giving someone something because it was convenient rather than buying them something specific, but I think the limoncello is ok, hopefully it wasn’t drunk from the bottle. I’m forever telling kids at school not to share water bottles (yes, it probably helps them and their gut biome etc but euw!)

I would have taken it in the spirit of kindness and appreciation that it was intended.

Backwash was my first thought too.

I am older now and over the days when we passed around a pint of Beam. 😎

But did she know it was open and some of it had been drunk?

OP it perhaps wasn't the best choice but I think you're getting a bit of a hard time here. Did I really just read someone imply that your seemingly completely normal DD may have drank the whole bottle and then filled it almost to the top with piss?

I mean I made some stupid decisions at 16 but this is absolute insanity.

The milk story makes me think she wouldn't mind. I would bring in something different for her like a box of chocolates and explain that you said you'd given it to her and your teen was mortified and explained they'd already had a glass. Then give her the other present instead.

I wouldn't give her another bottle of limoncello because there's a very good chance that either she doesn't like it at all or was fine with the partially drunk bit and then that's quite a lot of limoncello either to get through or to waste, especially if she's the kind of person who hates waste.

I agree with this.

She knows as well as you do it was a last minute gesture. Personally I would have been very happy to have received your gift!

I would think that it’s very strange (and I wouldn’t drink the opened bottle it would go to straight to the bin) . Tbh I wouldn’t expect anything apart from thanks.
If you realised that it’s obvious that the bottle was opened I would messaged her and would say sorry, you wanted to thank her but didn’t know that your teenager opened the bottle secretly, next time when you’d see her coffee would be on you. Something like this.
Because it’s true, you were in a hurry and couldn’t know

Genuinely delighted says it all. I would have been as well, assuming I liked limoncello. I wouldn't accept an open bottle of booze from a stranger in a bar but a trusted friend is different. My neighbour sometimes brings round a bottle of wine she has already started and it is always a treat.