If my friend’s Mom was in the hospital andit lost her hearing aids, does she have any recourse?

Your friend's mom could sue the hospital for negligence.  Negligence is the failure to exercise due care (that degree of care in this case that a reasonable hospital would have exercised under the same or similar circumstances to prevent foreseeable harm).  In order to prove negligence, your friend's mom will need to prove duty (of due care mentioned above), breach of duty (failure to exercise due care by losing the hearing aids), actual cause, proximate cause and damages.

Actual cause means but for the hospital would the hearing aids have been lost?  If the answer is no, actual cause has been established.  Proximate cause means were there any unforeseeable, intervening acts which would relieve the hospital of liability?  If the answer is no, proximate cause has been established.  Damages means the amount of compensation your friend's mom is seeking to recover in her lawsuit.  Damages would be the replacement cost of the hearing aids.  Your friend's mom will need to mitigate (minimize) damages by obtaining replacement hearing aids comparable to those that were lost.  If she were to purchase the most expensive hearing aids she could find as replacements, her damages would be reduced accordingly.

Prior to filing a lawsuit against the hospital, it may be possible to settle the case with the hospital's insurance carrier.  If that is not possible, which appears to be the case since the hospital is denying liability, proceed with the lawsuit.

If the case is not settled with the hospital's insurance carrier, the lawsuit against the hospital must be filed prior to the expiration of the applicable statute of limitations or your friend's mom will lose her rights forever in the matter.