Female cat mounting?

Hello, I have a 2yr old female cat who was spayed around a year ago. A few months after she started mounting a specific stuffed animal and kneading on it. I'd never seen a female cat mount anything so I was wondering what's going on? She meows while she's doing it also and if I approach her while she's doing it she'll run off. She used to do it every now and then but recently it seems to be a daily thing, sometimes multiple times a day. She's increasingly been doing this in the night while we're sleeping.

Additional Notes: She is a nervous cat, she will hide any time anyone comes over and refuse to come out. If they approach her she will hiss at them. She hides any time we open the door and is afraid of loud noises and easily scared. I've had her since she was around 8 weeks. She is however comfortable around my boyfriend and I, she especially loves sitting on his lap though she will occasionally bite. We have another cat, she's around 1yr old. She is very sweet and friendly even with strangers though she does not like being picked up. They're both eating normally and behaving the same as always with the exception of this odd mounting.

Has anyone else experienced a female cat mounting or know what this could be?

Mounting itself can be a dominance thing. But coupled with the kneading, it sounds like she's trying to comfort herself - maybe dominating the stuffed animal helps her feels tougher. The kneading is left over from nursing and is a comforting behavior.

Sounds like she may be a little stressed. Have you had any changes in the house - furniture delivered, new carpet, renovations? Even a small thing, like a schedule change, can trigger anxiety, especially in a timid cat.

We have a cat who spends about 50% of his time under our bed. He's a sweetheart but will react when a big truck passes by on the road.

Hopefully, whatever is causing her anxiety will pass soon.