I am offering her help. Probably the best advice she will recieve to be honest. Why tell her all these social networking sites when we all know (well at least I hope we do) that trying to sell stuff through a site that canot be SEO optimised is like flogging a dead horse.
I don't want to get in to a 'my advice is best' debate, but I am about to suggest that that my advice below will probably be the best advice the OP will receive!

I know that may sound arrogant, but it is based on the premise that we are in the same business as the OP and were in the position she is in (kitchen table start up) about 2 years ago.
Selling cards online is not easy - chrisandy mentions that he has built successful e-commerce sites for greetings cards companies, and he has, I've checked! But these are for the likes of Emma Ball, who are already well established players in the card - and related products - market. The OP will have to sell a lot of cards at £2 a pop to start to recoup the costs of hiring a web designer, SEO consultant etc
Selling through Etsy, Folksy, MISI and even ebay etc. is a much better route for her as, although she will be a small fish in a big pond, people visit these sites looking to buy hand made goods - going alone she'd be having to SEO her site up against these giants, it just aint going to happen. We sell to the retail customer through
Not on the High Street and we harness the SEO & marketing power that they put into this site.
I still think that SEO is not so important for selling cards. However, social media marketing has proved to be a huge hit with us. Our products are very visual and desirable, people like to read about them and see pictures of them. Using our
blog, Twitter and
Facebook Fan Page we have built a real following that has translated into sales.
Its horses for courses. SEO, I think, works well for some companies/trades - say accountants or plumbers where people may Google something like 'accountant Swindon' or 'Plumber TA18 7EF' as you can be fairly specific about what people might search for, but these people will struggle to define and make a social media presence - really, who wants to read an accountants blog (with apologies to all the acountants who blog on here!) However, searching for 'birthday cards', even 'handmade birthday cards' is far too generic, but as I said above, you can use social media marketing in this trade to good effect.
oops - looks like I've rambled on a bit! Hope the OP is still reading, and I'd be happy to help some more if I can (feel free to PM me if you wish.)
Jeff