
Hi, I have actually had Lyme Disease myself.
We were living in Germany a few years ago and caught it from my own garden (they can drop from trees)
I didn't notice the tick so it went undetected for some time.
I had no rash (usual first sign is bullseye rash) and began to feel like I had bad flu, not the coughing and sneezing kind but the joint pain, complete exhaustion, generally feeling awful.
I also have arthritis in my neck/spine/hips which I was seeing a specialist in Rheumatology and the Lyme Disease was a spotted in a blood test.
I caught pneumonia as my immune system was very low, I developed partial facial paralysis (Bells Palsy) which began like the worst toothache ever! I also have a mild heart murmur now too.
I had several courses of antibiotics and lots of other treatments too, and eventually I got the all clear!! :)
Now, I don't want what I've said to frighten you or your friend as I am fine now (just catch bugs/colds easier) and not all ticks carry Lyme Disease. But if your friend feels unwell and she can't shake it, then I would get it checked out.
As you can imagine, ticks did freak me out for a while, but I'm over it now and can remove them from dogs/cats if needed (mine have very rarely had them)
HTH
Paula