Nine years ago my DH died (my beloved German Shepherd had to be PTS five years ago, as well).
I have had one other relationship, but in truth will never move on. I now have another GS.
You expect your parents to die, they should, I certainly don't want to bury my children.
OP your baby is a new beginning for you, I am hopefully going to become a Nan in December.
You Mum doesn't want another Romantic Partnership, by the sounds of it, there will be no moving on from that life.
My DH's ashes will always be with one of my children, whilst they want him and if not with me.
I can manage my own life, I am the support system in my family.
That's what your frustration is about, not the ashes.
You think that her holding on to the ashes is symbolic of her not becoming independent and recovering, but getting rid of them may not help this.
Ave your baby, you will be stronger afterwards.
This may jolt your Mum into action, if not them set your boundaries.
Your baby may be old enough to be the one scattering the ashes, or as said, they can be poured down the toilet.
First pregnancy intensify any issues, especially around needed support, or having responsibilities.
You need to go with the flow for the next year and be honest with your Mum if she wants to much from you ( but not about the ashes).