A bit more info to add, the lump is still completely free moving, can get my fingers pretty much right behind it, i very gently pressed the front of it where the scab had fallen off and it felt very soft and yielding, like there may be fluid inside.
I dare not do anything else to it tonight since im still not entirely sure whats going on, i think it'll be a trip to the vets first thing tomorrow, and will see a different one than last time since she didnt seem to have a clue what she was doing.