Getting the hump

My flatmate has gone away for 2 weeks, which is great. Don't get me wrong, I really like her but its nice to have a bit more room around the house...or so I thought. My other flatmate has got his mum staying with us for the exact amount of time that other flatmate is away.
Now, I don't mind if people stay over, we all have peeps over, friends crash, guest call, its all cool and we are all fine with it, but I think your mum staying for two weeks is going to drive me mad.
This morning, I got up to go to work and she was in the shower in my time slot. We have one shower and there are usually three of us that have to get up roughly the same time, so my slot is 7am - 7.15 but if I over sleep my second time slot is 7.30 - we are running a very tight ship at my place but it works well.
Now flatmates mum is on holiday, she has nothing to do and last night she said she was just staying home today and she is in the bathroom kicking about at 7am!!! This is almost as annoying as senior citizens on the tube in peak hour , why do it, its not good for you, its not good for me it is just a major pain in my bum.
So she faffed about in the bathroom, do not know what she was doing in there, but 40 minutes later I got a look in.
Nothing like cracking the sh*ts as a way to start your day, luckily we have endless hot water otherwise I would of totally lost it.
If she does it again I am defo saying something, I have a job to get to lady and you better stay away from my shower time slot other wise I am cutting the water on you!