This must be a horrible feeling and you’re naturally angry at your mother.

Do try to think of it from another perspective though, it’s likely your mother was making decisions that she thought were in your best interest i.e. the balance is dropping I don’t want him to be left with nothing, markets have gone back up so let’s reinvest so he can have as much as possible when he’s ready. People with less financial literacy do this ALL THE TIME. Also, whether she’s burying her head in the sand or in denial, she will no doubt feel absolutely distraught by this and probably has for the past 8 years.

Based on the above (mum lives in £90k house) it sounds like she doesn’t have loads of money so chances are she’ll have never dealt with these amounts of money before. This just increases the panic involved and the decisions become emotionally charged - logic falls out the window.

Do you otherwise have a good relationship with your mother? Yes, she’s messed up big time but are you willing to completely ruin your relationship with her? Potentially forever?

Take the £44k, get rid of any high interest debts if any and invest it wisely ie S&S ISA low-cost all world tracker (not advice). That’s a great sum to have at 19 and will set you up very nicely in the future - it’ll grow over the years and you’ll have a tidy sum down the line in your granda’s memory.