How would I go about making a claim regarding bad canned goods?

The manufacturer and the seller (store where the can was purchased) are liable for both negligence and strict liability for this defective product.

Negligence is the failure to exercise due care (that degree of care that a reasonable manufacturer/seller in this case would have exercised under the same or similar circumstances to produce a product that is not defective.)  Negligence requires proving duty of care (mentioned above) breach of duty (failure to exercise due care since the product was defective), actual cause, proximate cause, and damages.  Actual cause means but for the contaminated food, would your mother have been injured?  If the answer is no, actual cause has been established.  Proximate cause means were there any unforeseeable, intervening events which would relieve the  manufacturer/seller of liability?  If the answer is no, proximate cause has been established. Damages means the amount of compensation your mother is seeking in her lawsuit.   

As mentioned above, the manufacturer is liable for a defective product.  The seller is liable even if the seller could not have discovered that the product was defective.

In addition to the cause of action (claim) for negligence in the lawsuit against the manufacturer and seller, the lawsuit should include a separate cause of action (claim) for strict liability against both the manufacturer and seller.  Strict liability means liability whether or not due care was exercised.

Prior to filing a lawsuit, it may be possible to settle the case with the insurance carriers for the manufacturer and seller.  If the case is settled with both parties' insurance carriers, NO lawsuit is filed.  If the case is settled with only one of the parties, only the remaining party with whom the case has not been settled would be named as a defendant in the lawsuit.  If the case is NOT settled with either party, both parties are named as defendants.  If your mother is dissatisfied with settlement offers from the insurance carriers, reject the settlement offers and file the lawsuit for negligence and strict liability.  If the case is NOT settled with the insurance carriers, the lawsuit must be filed prior to the expiration of the applicable statute of limitations or your mother will lose her rights forever in the matter.