Lending money

So I lend my friend 40 dollars she didn't say for what or I didn't ask but I didn't hesitate and lend it to her but I did ask when will she be able to give it back she said the next day or the following day. well its been over a week and she messages me like nothing. she's not a best friend that I hang out with she's just a friend I know but talk to her once in a while. Do I ask her when will she pay me, I know its only 40 dollars I honestly would give it to her if needed but what bothers me that it's been over a week that she said she will give it back and has not even mention anything about it or if needs more time or something. That's what bothers me more. And the thing that she still gets her nails done and talks about taking her kids to the water park that tickets for each cost 35 to 45 dollars. what should I do??