Childcare

So my best friend offered to watch my babygirl (6 weeks old) so I didn’t have to put her in a daycare. She has been watching her for 2 days now and now is wanting us to pay her $25 a day for the 3 days she planned on watching her a week. I would understand if she would pick her up and take her back to us everyday but we drive 15 minutes to take her there and baby is breastfed so I provide her with breast milk. Before she started watching her she made it seem like she’s do it for free since I’m her best friend but now is doing this, how should I nicely talk to her about it?