You need to complete Form C4
hmctsformfinder.justice.gov.uk/HMCTS/FormFinder.do
and take it, with a copy for the Court and a copy for each organisation you ask to be ordered to disclose information, to the Court. Call the Court first, as they are all dong weird things with court offices, so you may need an appointment, or have to come at particular times.
The Court fee is £200, payable to HMCTS.
Also complete form C100 as an application for a contact order. The Court should let you issue both together, and save paying the court fee twice.
The Court will want a written statement setting out the basic facts. There should be a template for statements on the above link.
I'd suggest as respondents you could suggest the Education Authority, and the DWP. You can ask for HMCTS to be ordered to respond (most likely success as they adminster Child Benefit) but you have to have a High Court not a County Court order because HMCTS is a Crown agency, so they don't have to comply with County court orders. Weirdly.
You can also ask for orders against other family members who might know, but TBH I'd just stick with the official channels.
Any solicitor who practises in this field should know how to do this. I think you should complain about the one you've seen. S/he is incompetent.
Once the Court has the address, the Court will serve your contact application (if your husband doesn't have Parental Responsibility, he should also apply for that, in form C1) on his ex. CAFCASS will get involved at that point as well.
He may get nowhere, sounds like she's hada load of time to fill the poor girl's head with nonsense, but it's worth a try, if only to be sure she's OK. Good luck.