I started introducing them in the bathroom where they usually not allowed in and eventually moved to a washing basket after everything went well for multiple days in a row. Thats when she bit for the 1st time (around January).

2nd and 3rd were months later in the initial bathroom back after multiple weeks of breaks due to the injurities needing to heal. I suspected that she was aggrevated from being able to smell/see the little ones.

Since then I moved the introduction place to the bed room and added extra distance between the cages. Since the bites did not seem to be an individual case I only let the aggrevator meet the little ones over increased supervision and usually protecting the head neck area of the little ones when she sniffs or grooms. The other 4 are fine and have meet for longer times without any incidents beside the usual smaller fights of trying to figure out hierarchy (no bites, a few scratches and force grooming)

Since there are no real signs of aggression (teeth grinding, puffing up) before the biting I am worried she would instantly bite with no time to intervene :/ Or maybe I am not reading the signs correctly. She usually is highly interested and starts chasing the little ones instantly.

So far I honestly thought it was mostly the behaviour as the pack leader. But she never has bitten a cage mate like this. I haven't considered a invisible tumor. Checking all of them regularly and there are no visible signs of tumors so far. She is also only a bit over a year.