Do I give tips to the Onsen lady?

We will be staying overnight at an onsen with dinner in the room. I think a lady will serve us dinner. How much tips should I give her or do I give her tips at all?

In Japan, tips aren't necessary no matter where you go or what you do. That said, ryokan and taxis are one of the few places where giving tips aren't that rare.

When checking in, a clerk will show you to your room and explain all the necessary things such as dining/bathing hours. When she is done with that, she will introduce herself and you are free to hand her the tip at this point. People say that by doing so, you might get extra attention while your stay.

The tip should be about 1000 yen per person/night more or less, and should be enclosed in a tiny envelope or wrapped in Japanese paper.

Note that the clerk who shows you to your room may not be the person who serves you dinner, but she is the person in charge of you, so all you need to do is to give the tip to her. In other words, if it's not the type of an accomodation where all this explaining and introducing isn't properly done, tips aren't necessary at all. Needless to say, if the accomodation fee is not too different from the 1000 yen p/p/n, tips aren't necessary either.

Enjoy your stay.