Your body has between ###-###-#### lymph nodes. Unfortunately, as a lymphoma survivor (Hodgkins), I know a little too much about them.
Based upon your message, I'd ask for an appointment with an ENT (Ear Neck Throat specialist) and get a biopsy. Get the entire thing removed (which will be painful) and have them biopsy it vs. a fine needle aspiration which collects only a small sample of lymph tissue).
95% of lymph node enlargements are the normal process of the body fighting infection. They get inflamed (not hard) as they're processing the invading materials. My lymph nodes that caught my attention were in my collarbone area. The only good thing that comes from those being swollen is Cat Scratch Fever. I knew before diagnosis I had cancer.
But the cervical lymph nodes (neck) are commonly swollen. The concerning part is that they're getting harder. Do they hurt? Pain is a good sign with lymph nodes. Mine did not hurt. Do they move freely? That's a good sign, too.
It's possible that recurrent infection is the cause, and it's the probability. For your peace of mind, follow your instincts and follow-up as needed. Get other opinions if you need to.
DON'T GET ON THE INTERNET TO DO RESEARCH unless your nerves are steel. You'll find everything scary when you need comfort.
Good luck. Please keep us posted on how she's doing. I don't want to scare you, but I also don't want you to dismiss it (like most people did, including physicians) in my case. I was fortunate to catch it early and have been clean for over 18 months.