Trying to introduce a 9 year old Australian kelpie to a 4 year old cat : Pets

My girlfriend moved in with me recently and bought her 4 year old ragdoll cat.
The cat grew up with a chihuahua and mother similar sized dog.
But the Kelpie and my other dog (rottweiler) are too big and scary for the cat, and it hisses at them if we try to hold them and bring them closer.
The reason I am coming here for help is that my Kelpie is almost obsessing over the cat.
She will go to bed, wake up, run around to the room the cat usually is in, and sit at the window all day.
I feel really bad for my poor little Kelpie:( I don’t want her to obsess over the cat forever.
Is it plausible that they could one day get comfortable with each other? Or am I introducing her to cats too late?
Sorry about formatting, on my phone.

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