Unfortunately the only way that she wont get access at 18 is if you set up a formal trust fund, with nominated trustees, that she cannot access until the age you specify.
Otherwise, with any savings account or ISA, it becomes her money on her 18th birthday, you will be locked out of any online access and removed as a signatory from branch access.
She will get letters as she approaches her birthday, so no hiding it, or 'hiding the bank book' as I see written on MN so often.
My DD was 18 last week so we are just going through this procedure with her S&S ISA and some inheritance money in a savings account. That has been moved to a maturity account, and I am no longer a signatory.
My online access to her ISA is stopped and she now has a Pin to set up her own online access.
All letters are addressed to her, so unless you are going to open the email of an 18yo, then you cannot stop them having access, except via a trust.
In terms of good accounts, just search for children's accounts and look at interest rates. Also check when they mature. My DD was 16 when inheritance was handed into our control, so we were limited on child accounts still open to her (some stop at 16) and she couldn't access adult savings accounts. But we knew it was only 18mo till she turned 18, so just wanted a reasonable rate. We went with Skipton.