The swelling could be an allergic reaction, has she been using anything different such as different underwear, washing powder, soap/shower gel, bath foam/oil, vaginal deodorant/wipes, lubricant oils, condoms etc...
Or has her partner which could have caused the reaction during sex?
Could be a yeast infection but there is often itching with this.
As for the bleeding could be some kind of cut as cuts down there tend to bleed profusely and could be aggravated during sex. Maybe it could have got infected hence the swelling? Any unexpected bleeding should be checked out though.
I'd advise her to abstain from sex until she knows what it is and get checked out asap. Get her to make an emergency appointment at the doctors or gum clinic if needs be. In the meantime she could get some advice from a pharmacy, most have areas you can speak to them in private. They will more than likely tell her to go to a doctor though or maybe give something like light hydrocautizone cream to help things in the interim.
Is there an NHS walk in clinic nearby she can go to?
http://www.nhs.uk/england/noappointmentneeded/ walkincentres/nearestsearch.aspx
Tell her to stick to light 100% cotton underwear and avoid wearing anything tight round that region and to avoid wearing tights for now so the area can breathe.