Is it hard feeling or soft and squishy? Can you move it around with your finger or does it stay still?
If it's soft, try steralizing a sharp small pin (sewing needles have worked best for me) over an open flame, and then insert it (gently!) between some scales in the lump. It's difficult because they wriggle alot but keep trying. Hold her against you as you do it. Once you've pricked the lump, squeeze ever so gently. And I mean gently! Do not force anything!
I've had some where a small amount of blood will come out and then the lump goes down and goes away aka blood clot for an unknown reason.
I've had others where it was all pus caused from anothers claw during climbing time. If nothing comes out, then it's a little more serious, and I would try Terry and a syringe extraction of the lump to see if he can get anything out that way.
Of course, if it's a hard lump, that's something I haven't dealt with myself, so see Terry if it is.
And also, I've never done the needle thing with a CND, only EWDs. So if you're not certain about doing that, go to Terry.