Question on bra's for young girls?

As most girls know, its nerve recking asking your mum for your first bra, and thats what it is like for me. I am worried about asking my mum for one, and also she is on a course so she can only come back on weekends, most of the time every 2 weeks, for a weekend. I want to ask her about it, however my family is all around us all the time, so it is hard to ask her.My dad does'nt mind me getting girl stuff and tells me not to be embarrased asking for something I need as a growing girl. So I am going out with him tommorow afternoon and was going to ask to pop into a shop which 1000% sells bra's. But, my mum wants to be with me when I get my first one, but i am to scared to ask her, but ok to tell my dad. I really dont know what to do. I think I really need one. Any advice to give me on whether to make this decision. All the help will be fantastic.