Agree with Jack412 on this, it would be sensible to get basic blood tests done as its not generally a good idea to try to treat major deficiencies without medical supervision because of the high doses and interactions and possible toxicity etc. But if everything checks out as normal, but she is still a bit rundown, then just taking a good quality multi-vit, plus a bit extra magnesium could help to prevent her getting deficiencies, particularly over the winter months. Also take a good look at her diet, make sure that she is getting enough fresh vegetables and enough protein. The other thing to look out for is whether she has any digestive problems, maybe she isn't really absorbing the nutrients from her food adequately, in which case she would need to have further investigation by her doctor.