I have many friends who had OHSS and it stinks, but it does take some time to go away. She needs to drink lots of gatorade and take it easy.
If she has very strong pain, faintness, she should go to ER and get checked.
I close friend of mine nearly died from a severed artery from retrieval (very rare) and the RE kept telling her to take it easy -- but she nearly died until she got into ER and they did an emergency surgery to stem the bleeding. This is not to scare you, she will know if it is that bad - she will be feeling very very bad.
But I would say 30% of the gals I know from my support group have had some version of OHSS and they recover within a week or two.
Wishing you luck, try to not worry -- I know its hard, it was very hard for me to worry about her health during my cycle.