This has been bothering me for quite some time and I was concerned at first she might have been wetting the bed.
The fluid is clear, doesn't smell like urine and the mattress itself is dry.
She is also toliet trained and rarely has an accident unless sick.
Anyway! It's apparently just "condensation" caused by the bed being on a cold tiled floor. It makes sense as the fluid is scentless and clear.
I have moved the bed onto a mat to add some further insulation between the cold floor and it's cleared it up.
Hope this helps someone that came accross the same issue!