GIRLS lacrosse equipment
You can purchase lacrosse gear locally, with Dick's carrying at least some options. Play It Again Sports also sometimes has lacrosse gear. Of course, there are numerous online retailers of lacrosse stuff, such as Amazon, sportstop.com, and lacrossemonkey.com to name just a few.
Also, Boys and Girls Lacrosse have different equipment requirements, and even some "shared" equipment such as sticks, are different. US Lacrosse has a PDF guide and other information about the various types of required and optional equipment.
US Lacrosse rules require youth Girls to wear the following:
Goggles/Helmet. Helmets are a hotly debated topic in girls’ lacrosse (see NY Times article) but eye protection is required either way.
Mouthguard. Cannot be clear or all white (i.e., must be colored so that refs must be able to see that you have one in).
Stick/Crosse. There are a bewildering array of options (and price points), with all sorts of marketing claims. Ask your coach if you are really unsure, but here are some current recommendations for sticks that your player can use for years:
Midrange
https://www.lacrosseunlimited.com/stx-fortress-700-girls-complete-stick.html
Top End
https://www.lax.com/lacrosse-equipment/stx-exult-pro-lock-pocket-complete-stick/172895.html
https://www.lacrosseunlimited.com/gait-apex-girls-complete-stick.html
https://www.lacrosseunlimited.com/stx-lock-pocket-complete-stick.html