My 18 month old sleeps on a floor bed as I have a wrist injury and was unable to lift her in & out of a cot. Since she’s sleeping in a bed instead of a cot, can she sleep with a pillow or is she still too young at 18 months old? She keeps taking couch cushions or my pillow to sleep on & I have to take them away from her.

Red Nose recommends keeping soft bedding out of the cot & to withhold a pillow until a child is in a bed as daughter is.
It is safer to wait until the child starts to sleep in a bed before introducing a pillow or other soft bedding.
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows

Red Nose has the following information when moving a child to a floor mattress.
Ensure the mattress is positioned away from the walls as young children can become trapped bet ween the mattress and wall. A child’s mattress needs to be firm to prevent sleep accidents.
Keep the area around the mattress clear of soft toys, bean bags, plastic bags or similar objects that a young child can roll onto. Soft objects could mould around a young child’s face, resulting in suffocation.
https://rednose.org.au/article/where-to-sleep-a-child-who-has-moved-from-a-cot