Dog aggressive toward other dog when my husband is out of town?

I have an 8 year old female bulldog (Abbey) and a recently rescued approximately 4 year old female AmStaff/Manchester Terrier mix (Tulip). We don’t have any history on Tulip except that she was transferred from a high kill shelter in Kentucky to a rescue here in Maryland. Generally they really like each other, play together, Sleep next to each other, and such. Tulip does show some characteristics of separation anxiety when there aren’t any humans in the house, but it’s much better than it was when we got her back in March. There have been a handful of instances where Tulip (40lbs) will attack Abbey (70lbs). Recently I noticed that , except for one instance, this only happens when my husband is out of town. It’s odd, like separation anxiety from him causing Tulip to want to Velcro to me and getting stressed if Abbey is closer. But not always, as I said usually they’re just fine. I’m wondering if anyone has ever encountered this before and if there is anything we can try to alleviate it.