My heart goes out to you because we aren't the only ones that suffer a loss.
We lost our beloved Zachery, our Pom...at the time we had a 4 yr old Lab named Lucy.
Well they were best buds and sweet Lucy just adored her little Zachery.
When he passed away we had a terrible time with Lucy, she would look at us as though we had killed her best friend.
They say animals know what's going on but in this case I don't think Lucy had those instincts.
She wouldn't swim or play with her tennis balls...didn't care about her meals, ton walks she just barely moved along with no interest.
I was about a month she started to come around.
It was then we were searching for a new rescue and when Bubba came to live with us she didn't know what to make of him.
Today they are very close but you just have to give Lulu time, lots of love and try to keep her busy.
Good luck, she'll be fine eventually.
Sher