Introducting new rat friend after partners death

Question
Hello. I have a female rat called Ziggy (approximately 1.5 years old). Her mother and father came from a pet shop. I first had the mother and father in a cage together. They had babies but I only kept Ziggy. The mother died about 7 months ago and the father died about two weeks ago. Ziggy was really close to the father and became depressed after he died. They were kept in the same cage together. So I bought a one month old female rat to befriend Ziggy.

As soon as I introduced them, Ziggy jumped on the little one and bit her (drawing blood). I put them in separate cages and put the cages next to each other so they could get used to each other. They've been like that for a couple of days but Ziggy still tries to attack the little one through the cage.

I just read your advice today to someone else about keeping fresh airspace and then introducing the rats in a neutral place after two weeks. Do you think I should separate the cages again & try that?

About mingling with the family - I let Ziggy out every day to roam around the study (where the cage is kept) and also the lounge room.

Answer
Unfortunately Ziggy displayed the very worst behavior a rat can have toward a new roommate - blood is always a bigggg problem! What I would do is separate the girls completely and give each a bath. Sanitize and rearrange a neutral location (bathtub, bathroom, sink, countertop, etc.) and let the younger girl run around for a bit - I'd say at least 20 to 30 minutes, but the longer the better. If she has a hammock, house, etc. that she has been using, I would also put that out for the little one to play with. After she's calm and comfortable in this space, put out a little pile of food or treats and then let Ziggy in to play. Now that this is the new girl's area, Ziggy may be off guard enough to re-start introductions. If she instantly rushes the baby and again draws blood, I would have to accept that Ziggy now prefers to live alone and you need to get a new (docile, younger) roommate for your newest girl and come to terms with having two cages with rats! If she allows the interaction, allow the two to mingle for as long as you can, clean and sanitize what will be the community cage, re-arrange it, wash ALL cloth bedding (hammocks, blankets, etc.) and bleach (or vinegar) all hard surfaces. Then you may begin putting the girls in the community cage starting first with your new girl (allowing her 5 minutes or so in the cage to rub her smell on everything) and ending with Ziggy. Keep a very, very close eye on them.. things can go poorly in a heartbeat.

Good luck.