If a follow told me that I am not collecting enough, I would assume that she means that she cannot feel my axis. Some follower beginners without good sensitivity need an extremely strong, defined axis, so I would not get offended, but would just change my style for her and give her a strong, pronounced, exaggerated axis so that she can really feel it. Usually I can tell if she is not feeling my axis, because her steps will "drift" a bit, so I think this is my fault. On the other hand, marking the axis too strongly will sacrifice smoothness and comfort, so it needs to be adjusted to more subtle again after dancing with a beginner. Sometimes I see an advanced dancer with an advanced follow marking the axis too strongly and the follow isn't enjoying it and I can tell he has spent the last hour dancing with beginners.
Technical point: Collection is either stylistic, or a learning technique before learning to "project your axis." Once you can project your axis, in my opinion, collection becomes largely unnecessary, but it doesn't hurt to revisit it at times to strengthen balance or to use in more advanced moves like some subtle close embrace colgadas or leader's back cross to pivots that can be extremely difficult without collection.