Sadly alcoholics lie about their drinking. They sort-of have to. If they honestly admitted to themselves and others how much of a tragic farce their lives had become due to booze then it would be very hard for them to justify going out and getting pissed yet again. So they lie about it. Most of all, they lie to themselves about it. But they also lie to those around them. Try not to take it personally. It's nothing to do with you.
But this automatic lying leaves people in your situation with a simple choice. If you think she's been drinking - and I'd bet dollars to donuts you are phenomenally good at spotting it as you've probably seen it hundreds of times before - then you can either confront her and get lied to (and/or drawn into yet another pointless argument), or you can simply believe your intuition and act accordingly. Whether she admits she's drunk or not does not change reality. If you think she's drunk, she's drunk. No need for discussion. No need to argue over whether she is or whether she isn't.
The Social Services involvement is, I'm sure, a worry. I've been there with my ex but I had the advantage that by the time that Social Services got involved she'd already moved out albeit we were sharing care of our children 50/50. But it was a horrendously scary time nonetheless.
Social Services has a remit to try, as much as possible, to keep families together. But they have to balance that with a duty of care to try to reduce the risk of harm being caused to children. Make no mistake - an alcoholic parent is a shoddy parent because that parent's reactions and behaviour will vary massively depending on blood/alcohol content.
Social Services gave my ex a lot of opportunities to sort herself out. But you can't force an alcoholic to stop drinking. In the end Social Services helped me to come up with a plan to ensure they our children could still see their mum when she was sober but to have backup plans in place for when she wasn't. It wasn't perfect but it was an honest attempt to make the best of a very shitty situation.
All this happened five or six years ago. At best, my ex now spends a few weeks, sometimes a few months, sober. And then she spends a few weeks, sometimes a few months, pissed out of her skull. As my DCs have got older they've got more reluctant to have much to do with her. I've repeatedly reminded them that their mother's drinking is nothing to do with them. It's not their fault. She'll drink for reasons that are entirely her own.
When they were younger then I tried to manage how often they saw their mother. Sometimes it worked well and they saw her a couple of times a week but, sadly, it never lasted. Now that they're a bit older, a bit more self-reliant and a bit more vocal about what they want, I'm letting them take more of a lead although I do reassure them that whatever they decide I'll back them up and that they are allowed to change their mind whenever they want.
I'm not saying that your DW will end up like my ex. I never thought it would end up like this either to be honest. I would very strongly recommend being honest with Social Services about what is going on and to take their advice seriously.
After the meeting it is well worth dropping the Social Worker a written note along the lines of "Thanks for your time, just to recap - you said x, y, and z. I committed to doing this, that and the other thing. You agreed that you will come back to us by so-and-so a date with advice regarding blah-de-blah and that we'll meet again in three week's time." Social Services runs on paper and most Social Workers are hideously overworked. Don't rely on them to note everything down correctly. Any reports they send you, do fact-check and (politely!) correct as needed.
Do ask their advice about how to deal with situations like the one that prompted this. Get the Social Worker's phone number. Give him/her a call when you can get some time to yourself. Ask how you're supposed to deal with this.
I found Al-Anon very helpful but, to be honest, I found one-to-one counselling (arranged via my GP) even more useful. Because, god knows, trying to raise kids with an alcoholic co-parent can be downright horrible. You need, and deserve, some help and support.