Tenant has posted on social media that she's moved but I've had no notification

Universal Credit

So the tenant I've just had to replace locks and windows for (because her ex broke in while she was away visiting family) has now posted on social media that she's moved. I've had no notification from her that she's moved and she's not answering my messages or calls asking what's going on and what's she's done with the keys.

I'm hoping for some pointers as to where to go from here? Can I just ask my maintenance guy to go round and check if she's put the keys through the door or will I/he get into trouble for entering? (I'm assuming so).

What happens re the dwp payments? She's two months in arrears and they only just started paying a monthly arrears amount so will that stop? She's given no notice so when would dwp consider the tenancy ended?

I'm trying to convince myself I should be relieved since it's turned out she's not very reliable but since my other tenant is also wanting to move on, I'd really rather get this sorted asap before I end up with no income but extra bills to pay (council tax, higher insurance) :(