My FIL passed away on Dec. 16th, and my MIL has lost her will to live. Is this common?

MIL and FIL have been in AL and MC for 2 years. Before that they were in IL but with assists such as medicine supervision, meals provided, etc. Before that they lived at a senior apartment complex near us and we provided support as needed. This has been an 11 year journey with dementia and Alzheimer's. MIL's dementia has been worse than FIL's the whole time, with her becoming violent toward him, prone to UTI's, delusions, paranoia's, etc and became a flight risk 2 years ago, prompting her move to MC. The place where they live has houses, about 12 houses with 8-12 residents in each house, and he was in one house--AL and she was 2 doors down. We separated them because of her violence toward him and his need to "control" her. We felt he needed to get a respite from his caregiving too. Even throughout the pandemic, they considered him part of their "Pod" and allowed him to visit daily. We were not able to visit until October so we were not picking up on some of the subtle declining in his cognitive abilities. We were quite surprised and started to think about memory care or the step in between for him. This first week in November, his brain quit telling him how to walk. He took a fall on Nov. 11th. We took him to the the hospital where there they ran every test imaginable looking for stroke signs, etc. Nothing. They sent him to rehab to try to see if they could help him learn to use a walker to help him. While in the hospital and in rehab he suffered from hospital delirium. Every day when my husband visited he wasn't sure if he'd see "Nursing Home Dad" who couldn't; communicate more than moaning/crying/mumbling and laying in bed, or "memory care dad" who was interactive and sitting in a chair. The NHD days outnumbered the MCD days. He was also refusing to eat or drink, losing weight and muscle tone. After 23 days, the care team decided to move him back to his AL with the stepped up care to see if being back in familiar setting would help with the delirium, and help inspire him to eat. We also felt that seeing mom would help.
In the meantime she and several in her house were tested positive for COVID but all had very mild symptoms. When he returned to the AL, she was on the last day of her quarantine. but they tried to reunite them the next day. Neither recognized the other. :-( Both had convinced themselves that their spouse was gone, their family was gone, etc. even though my husband was visiting daily. FIL continued to go downhill, refusing food and water. We called in Hospice. He died peacefully in his sleep on Dec. 16th. Unfortunately we were not able to be there because on Dec. 12th we had both tested positive for COVID and could not be in the AL houses. We had to postpone the graveside service till December 28th when we were all out of Quarantine.
Since that time my husband has visited his mom, but she is in bed most of the time. We had gotten her qualified for hospice in December also, so the hospice nurse and aides have been keeping good tabs on her condition. She has become increasingly withdrawn and has been sleeping most of the time. The past week she is refusing food and most liquids. Her vitals are still somewhat strong in spite of that. We are doing all we can, to encourage her. My husband took some more pictures and familiar items over there on Sunday but she did not acknowedge them. The hospice coordinator thinks it is only a matter 2-3 weeks if she continues on this path. It appears she just doesn't want to/cant wrap her broken brain around life without him. They have been apart since Nov. 11th, even though he did't pass until December 16th.
I guess I wanted to know if others have experienced something similar. I never in a million years thought he would pass first. I think if she had, he would have had the will to go on, but I don't know for sure.