I have in my possession the ashes of my biological mother, who died of breast cancer. How can I use them to help in my own battle?

There's an old Roman and pagan tradition that uses something of the ancestors as guardians. They were often on the outside of the dwelling to guard the residents, yet also at cross roads of those less fortunate.

Must note they should be well though of and the shrine blessed yearly. Samhain would be best. You should know why then.

Lookup "Lares"

https://en.m.wikipedia.org/wiki/Lares

Pick something she herself would like.

I don’t know what your personal battle is but we all have them.

My mom passed from cancer when I was fairly young. It was a crossroad in my life as it forced me to confront how little time we get in this life. Her memory gave me the courage to get off my ass and do something with my life.

Let her ashes or memory or whatever you’ve retained of her be your guide though your battle. Even in death, your parents are still a profound influence on your life. I wish you luck

Update: I have ordered a replica of the Venus of Willendorf (the earliest carved mother goddess image, and a good resemblance to her), and some purple candles (she used to say that she owned everything purple, but we were allowed to use it), and will be building a permanent shrine to her quite soon.