A few months ago I had two different experiences within 24 hours. The first one on a Saturday evening, the second one on a Sunday morning. I must say that I haven't had many ghostly encounters yet, but I'm pretty sure that what I experienced must have been related to paranormal activity.
The first experience of the two was when I was lying in my bed, wide awake. My cat had joined me on my bed, like she does often, and my mom came into my room to check on me. She always does that. She thought that maybe I couldn't sleep because of the cat, so she took her out of my room and closed the door. The weird thing was, though, that moments after my mom had taken my cat out of my room, I felt pressure on my pillow, just as if a cat was walking over it. I touched my pillow where I had felt the pressure, but there was nothing there that could explain the pressure. If it was a ghost cat, I'm not sure whether it was our own deceased cat or some random cat that decided to pay me a visit, because our own deceased cat never jumped on my bed, because she thought it was too high. (I have a 90cm high bed and she wasn't a very active cat.)
The next morning was a Sunday morning and we were going to go to church. I was looking trough my jewelry to find something that suited my clothes, when I all of the sudden smelled something I hadn't smelled in quite a long time. It was the smell of my deceased great-grandmother and I immediately thought of her when I smelled it. She loved jewelry, so maybe she was somehow attracted by it. Some pieces of my jewelry had once belonged to her, so I smelled them afterwards to make sure I hadn't just smelled the jewelry, but I didn't smell her smell anymore. It had also really felt like she was there with me.
What a beautiful encounter you had with your great grandmother. It seems she really was there with you while you picked out jewellery to wear. Jewellery is such a beautiful way to connect with loved ones on the other side. It sounds like your great grandmother takes pleasure in seeing you enjoy her much loved possessions.
The cat is very intriguing. I grew up with cats, and we all felt ghost cats on our beds sometimes too.
Because both incidents happened days, or even hours apart, it's possible your great grandmother is looking after your deceased cat on the other side.
I know the cat wasn't very active, and your bed is high, but even so this cat's physical limitations may no longer affect it in the spirit realm. That said, resting on your pillow indicates this cat may feel uncomfortable, possibly with it's new life after death existence. Cats always seek refuge in high places when they feel uneasy or unwell. Cats will also seek refuge near your head, on your pillow, for the same reasons.
I feel it's possible your great grandmother is taking care of this cat and helping it to adjust to the spirit realm. Don't worry, all animals must go through an odd adjustment period, people too. Take comfort in knowing the cat feels safe with you on your pillow.