Hi. If she had shares held with Campbell O’Connor they would have been held in one of three ways. Important to find out which one was the case so you know how to proceed.
1. Held in nominee digitally. This means there is no share Cert. Fewer companies are issuing share certs now. They will be registered in the name of the company but assigned to your mothers account
2. Held in nominee in share Cert form (as above but in paper form). This is unlikely though unless it is a very old investment.
3. Held for safe keeping. This is normally where the stockbroker holds the share cert in the clients own name in a safe somewhere. Again unlikely nowadays.
In any case the shares or value of shares if sold might be held now with Cantor Fitzgerald
If they were held in your mothers own name she should have received any correspondence about the shares/takeovers/dividends/stock splits etc directly from the registrar. If she has not received any info then they are more than likely held in nominee.
I would suggest finding out who the share registrar is for the stock (Computershare etc) and contacting them as they might indicate if there is any in her own name.
Contact Cantor Fitzgerald as they will have a record of what came over from COC.
Does your mother have any paperwork from any of the above or a copy of the share Cert or an account number? This will help anyone you contact to retrieve any info.