I asked the same question a year or two ago and was told that if you mix with normal compost it would be ok. You will obviously still have to feed the rose as the ashes were inert. Lovely picture of your friend and a lovely way to remember her.

Ah, I'm so sorry about your loss. I've been through it many times and it never gets any easier. I love the idea of planting a commemorative plant. Did Cleo have a favourite part of the garden? If so, could you plant straight into the ground then sprinkle the ashes round it?

So sorry you have lost Cleo; she was a beautiful girl. It's heartbreaking I know. My dog is terminally ill and we will have to face the dreaded inevitable at some point. What a lovely memorial for her though and I hope it gives you comfort in your sorrow.
All the experts say it's best to plant a rose in the ground but I planted a peace rose in a large pot last year and it's doing great so far. If it was my decision, I would go for a pot so that I could take it with me if I move.

So sorry, she was a lovely girl, I have pets area's here and always a special tree, shrub or feature of some sort...

When we lost our Golden Retreiver called Gemma . I searched for appropriate plant . To my joy I bought a Rose called ' Gemma ', planted , where we buried her in our garden . It is a fantastic rose , is small pink flower clusters , and flowers for ages . She will always be remembered , as part of our family for nearly 14 yrs ( It is also called Fairy Rose ) See on my pics

Are you intending to mix the ashes with the compost? Just a thought, but you will probably eventually want to repot, so you might think about burying them in the pot in a rotproof container that could be moved on if necessary?