OP, did you ever get the taxi money and the £5 for the clothes she wanted to buy her mum from Primark? Somehow I doubt it.
When you're telling (not asking) her to transfer the make up bag money, tell her the £8 (and state clearly her £3 share of the taxi plus the £5 trousers) is also to be paid so she needs to transfer a total of £17.60.
Be clear. Be polite. Be firm. No sorry's, no "I'm afraid.." no "Could you please...?". Be nice and straight as, well, you know she can get so confused, right? 
Anything further back that she owes I would probably write off unless it's a very clear, specific amount lent to her, or she will claim no knowledge of it.
That said, if she even starts to try to get out of the £17.60 then start listing off the monies you've paid out as far back as you can recall. She needs to know there is actually a financial cost to you that you're sick of bearing.
And never have any spare money as far as she is concerned again!
When she asks, laugh and say, "Ha ha! Not likely pal! You know you'll never pay me back!"