You're welcome! The higher the coverage of the foundation, the less "forgiving" the colour match will be, and daylight will make it obvious if the match is wrong. If she really can't get to a counter, I'd be inclined to get her to take a close-up, high-res photo of herself in daylight that you can take with you to drug stores/make-up counters. I'd then look at good drugstore foundations and aim to buy 2/3 shades of the formula you like the best (one that you think is the best match, and then one shade darker and one shade lighter).
Depending on how dark her skin is, I'd suggest the following. At a big Tesco or Superdrug, you would probably pay £30 for 3 shades so it's a safer option than spending the same on one tube of department store foundation:
Bourjois Healthy Mix Foundation (black cap, not red-capped serum version) - this is great for olive toned skin and lasts very well in the heat, but possibly a bit pale.
Revlon Photoready Foundation - this has the fullest coverage, is long-lasting, and comes in darker shades than the Bourjois (the nude, natural beige, medium beige or golden beige might be appropriate - the others all look too pink to me), but might be a bit too heavy and shimmery compared to the Bourjois.
Rimmel Wake Me Up Foundation - a bit darker than the Bourjois, and not my top choice as it can look very glittery outside, but many people do like it.
She will need Translucent setting powder over the top, but any old one will do as long as it's finely milled (so not chalky) - No7 Creme Touch is good.
Foundation, blush and powder brushes are pretty much essential for applying wedding make-up - does she have any? If not, I strongly recommend the Real Techniques Expert Face Brush for foundation (flawless finish and very to use), but cheaper own-brand brushes for powder and blush (the Boots ones are good).
For eyes (if she needs stuff), Max Factor Masterpiece liquid eyeshadow in "classic pearl" (to highlight the browbone) and the dark brown colour (for the eyelid itself) would look beautiful and should last all day without smudging. Best applied with the sponge-on-a-stick that it comes with, and blended with any old eyeshadow brushes. Avon does a pencil eyeliner called Supershock in Blackberry that would look beautiful over the top and lasts very well - it's about £2 on ebay. Any waterproof mascara would be fine, but I highly recommend No7 Lash Adapt (not waterproof, but water resistant) if she's looking for one of those too.
For blusher I'd look at No7 Soft Damson as you can't go wrong with that on anybody (IMO), or any of the pinkish Bourjois shades.
What kind of lipstick is she after? Strong/subtle, shiny/matte, pinkish/reddish/purplish?