Should she pay �10 more?

I started saving up for my phone. I then had to give all of the money to my mum since she was short on money for things. She paid back the money and she said once you've chosen the phone you want, I'd buy it for you. I've saved up enough for the phone, but I need to pay �10 for credit. Should I just save up more or should my mum pay for it and I'll pay her back after that?