It's a "play-date" ask her if she has anything to do. If she says no then accept it. Don't write a note or send her a text, we hate that. Be forward.
Well, for starters don't call it a "play-date" unless you're both under about 3 years old.
Just how you get a date with any other girl-ask her out.
ask her to go out with u
== ==
ask her!
You ask her out.
ask Her on a date
you ask her?...Or you ask her best friend if she likes you and is she allowed to date.
ask her on a date
If you can date, ask her out.
Ask her out.
On the date? Ask her about herself.
Ask her out on a date.