After finding out my mom, who has dementia and is in Assisted Living, has been taking her dogs for a walk on her own, without supervision, we have decided she needs additional supervision, so we are moving her to Memory Care. We know this will be very traumatic for her since she can't have her dogs with her. She's become very attached to her dogs after my dad passed 6 years ago. They have become her security blanket. How long may this take for her to forget about her dogs and hopefully make some friends?
I know that when a 100 year old lady that I visited regularly who had a dog in her home had to be moved into an assisted living facility, a friend of hers took her dog to care for and would bring him to see her in the facility every week or so until she passed. Both were always very happy to see each other.
Also, please have tempered expectations about her "making some friends" in MC... dementia breaks people's brains so that they can't function socially as before. If the facility has an Activities Director, get your Mom on her radar so that the staff will try to get her more engaged.
It's not a replacement for the animals she loves, but there are some very realistic robotic dogs, which could become her new security blanket. Google it.
If mom gets depressed and angry with you, do not fall into the trap of trying to fix it for her. You can not. Her aging body is failing her, and she needs the care and safety of a memory care facility. As her dementia progresses, you can not reason with her or explain anything to her satisfaction.