I don't post in AIBU very often so please be gentle. I will try not to drip feed.
Allegedly, six months ago, I agreed to go back to my former job to cover employee/shareholder absence. The employee/shareholder is a friend of my mothers and asked me via my mother if I would help out. I said yes.
I do not remember doing this, but it is not beyond the realm of possibility that I did. It is something I would normally agree to.
Last month, I discovered I could make money through a hobby. I pushed this as much as possible and basically took on full time hours doing this, forgetting I had agreed to work.
(It was 12 hour shifts, 6 days a week for two weeks - for £5 p/h - in the interests of of not diverting the thread I am self-employed and will declare the £5 p/h through that. I am aware £5 p/h is not the NMW and is illegal but the person I am covering for has a share in the business and receives a % of the profits in lieu of wages. She offered me £5 p/h and I agreed because she is a family friend)
Now, getting to the point, because I forgot about this, I took more hobby job work than I could manage, so ended up getting up early/staying up late to manage hobby job and 12 hour shifts, which made me tired and grumpy and a bit snappy and I probably definitely made a few digs about family friend taking the piss out of me.
My mother commented a few times it would make me ill and asked me to consider giving up hobby job. I said once I'm not working 12 hour shifts, 6 days a week, it would be manageable. She then mentioned college, worried I would not return after the holiday in favor of hobby job and I assured her I would and reminded her I am not at college 12 hours a day, six hours a week, so it would be feasible to do both without cutting my sleep down to 4 hours a night, like I have been.
Family friend already decided to take their holiday two days early, without asking me, leaving me with no option to cover them, so their business partner (a friend of mine) wasn't left up shit creek.
Family friend has now added an extra day to their holiday, again without asking me. I blew up and told my mother family friend is taking the piss. My mother got the brunt of my temper because family friend always communicates through her and never contacts me directly about work/holidays even though we have contact regarding other things.
I told my mother, in no uncertain terms, I have far too much to do to cover their friend's ass constantly and then asked my friend. My mother defended family friend and then started sending me text messages telling me I should give up hobby job as it's making me nasty when I never used to and I should go and work for family friend for £5p/h as I am not making NMW at hobby job anyway.
She is now not speaking to me because I told her to go away and leave me alone.
FWIW, neither the business owner (my friend) or shareholder (family friend) NEED me to work there but would let me if I wanted to. For £5 ph 
Now, I never wanted hobby job to be my FT income and I know in terms of work/profit it's not economical but it is something I could possibly build up to a full time living IF I wanted to, though I have never expressed any interest in doing but AIBU in thinking my mother has ulterior motives for asking me to quit?
I just can't work out what they are? It's nothing to do with me staying on at the £5ph, neither the family friend nor business need me there. They would tell me if they did.
And if you are able to follow of that, well done! I couldn't think of a more simple way to explain things without drip feeding.