Maybe sit down together & have a look on LH as long as she knows her sizes, she could choose some lingerie that she would feel comfortable in a nice bra & thong set to start off with, if not a thong then go for knickers, at least ordering from LH she doesn't have to try them on in a shop, but as always she has to feel comfortable from there she will start to feel more than sexy.
Hope this helps a little, sorry that is all I could think of.
I know I shouldn't say this as this is a lingerie site but LH might be a little too imposing? I always found somewhere like La Senza was a good place to start. It's not overtly sexual but they still have sexy things. Not sure where you could look now though.
if you want my advice a sexy woman is a confident woman and if you just throw her into revealing underwear then she WONT wear it! my boyfriend bought my a stunning lingerie set for my birthday it was all wrapped up and looked grogeous but it was a lace bra set and it didnt look anything like it did on the underwear model. A woman knows her body and she will never feel comfortable in something that the knows wont show off her best assets - my advice is that she needs to feel sexy in herself. i wouldnt just go buy her something that you like because u could be completely wrong - she needs to know how to choose lingerie to suit her body shape and flatter her curves. eg - if you have a big tummy corsets are a great wat of pulling in the tummy and giving a flattering waist - maybe you should spend time researching how to dress for her body type or what will flatter her figure - just because a corset or chemise is covereing her up it doesnt mean it wont look sexy - the best advice i can give is let her learn how to feel confident first. ive found an article here that has afew little tips for flattering shape http://blushboutique3.wordpress.com/underwear-how-to-pick-it-for-your-body-shape/
this is just my opinion but i hope it helps :) x