Dog coming into cat household- subtle prey aggression
Hello, seeking some advice here. We have 2 very well behaved sweet female cats. We decided to adopt a dog this weekend. She is 6.5 years old according to her teeth. They are not sure exactly how old but they gave her her age based on her teeth. She just had puppies about a month ago and stopped nursing a week ago. She is pretty well behaved for likely being a stray, but also very skiddish and under confident. We brought her home last Saturday. She’s currently on 2 gabapentin twice a day. Sunday morning our cat was walking by her and did a little flip after rubbing on some boxes nearby and she ran at her. Didn’t try to bite but got up suddenly and ran/ lunged at her. Definitely freaked us out but it was only the first day. Everything has been fine since, the cats have warmed up and she has a little as well, tolerated the cats anyways. She won’t look at them and whines when they’re around sometimes but hasn’t acted out since the first day. Just now she heard a noise by her food and water bowl and got up to look and it was my cat drinking water form her bowl. She did not look pleased and I told her to stop it and she walked away. She then went back to her bed heard the cat drinking water again and slightly lunged at her but didn’t get that close.
My question is, is the gabapentin clouding over her prey driven aggression towards the cats? Or is it making her more jumpy/ flinchy? My biggest fear is our cats getting hurt because we overlooked her prey driven instincts. She’s in a very fragile state of her life after giving birth, missing her babies and a whole new environment in medication. She’s a very sweet dog and well mannered but I could never forgive myself if something happened. Will the weirdness wear off eventually or should we call it and give her back to the shelter? She’s getting spayed on Friday and we are currently fostering her through her medical procedure.