Accidental Overstay

Awkward!
Mother in Law has been living with us for a while. Mid 2011.
Initially an ancestry visa by way of Canadian Citizenship.
I am originally UKC and wife also now naturalised UKC (Also US)
Long story short MIL did an extension of visa in 2018.
Wife and I understood it to be ILR had been applied for at that point.
Apparently not. It was FLR(O) further leave to remain.
BRP had expiry in Sept 23.
First we became aware was NHS letter that access to NHS was now on a cost basis!!
So we are in overstay territory! Accidentally but is what it is.
Trying to ascertain next step or what the route to either ILR or UKC from this point might be or some intermediate visa again.
Looking for professional advice but where from? Google is returning immigration firms that seem to be weighted toward helping asylum/refugee cases.
Thx in advance.

I don't think you can have British citizenship without ILR here, so route to it is ILR.
How to get there is another story.

Possibly you could consider applying for ILR (LR), using her 10 year stay between 2011 and 2023?

But you need to regularize her stay first. I'm not sure how - others will advise further.

By the way, we can't allow any solicitors advertising/recommendations on this forum.