Asking for money???

How do I politely ask this lady to pay me $150 this time I watch her dogs? They’re out of town for three nights and want me to stay overnight at their house and come during the day to let the dogs out.

Last time she only gave me $100 and we hadn’t handled it professionally (because it was a friend of my mom) so I didn’t find out until she paid me, and they also paid me more the first time I watched them.. so I thought it would be the same.

Help me out if you have any experience telling people how much you want for services. Thanks!