Hi, I am Dr. Jeff. I will try to help you. Please feel free to follow up if any more information is needed. Allergies are certainly a concern. In some cases, you may see a response to Benedryl (diphenhydramine) at a dose of 1 mg/lb twice daily. While they results may not be dramatic, it may help enough to provide some comfort and rest.
Other issues like respiratory infections are also possible. This is especially evident if there is a green/ yellow ocular or nasal discharge. Most of these issue will respond to antibiotic therapy prescribed by your vet.
Keep in mind, there can be some underlying issues that can predispose an aging lab to these types of infections such as an infected tooth root, mass/polyp in the nasal passages, foreign object lodged in the nasal passages, etc.
So, I would try the Benedryl to start. If this is not helping or she declines in any way, I would seek veterinary attention. Antibiotics are a possible treatment and if these are not helping, then more aggressive test may be necessary such as a nasal culture, tracheal wash, rhinoscopy, xrays, etc.
I hope this helps and gives you direction.
Thanks
Dr. Jeff