What in particular is your friend looking for. I generally source things from kensfish, big als, amazon, GLA, dr fosters, petstore.com and lesser on [Ebay Link Removed] There are plenty of shops also in our area. the directory i maintain pretty much lists any and all in NY, NJ and CT.
I would suggest you get her all the plants she may need through the forum and then you give them to her. Cheaper than stores, better quality, and support fellow hobbyist. If you let me know of a few plants you are looking for i might be able to help you.
Fair warning to avoid emersed grown plants as they will take some time to transition and will look somewhat different afterwards... Best to focus only on submersed plants. This is one of the turnoffs to buying at retail since most shops get their plants from farms in florida that grow them semi / emersed as it grows faster.